Education of Left-Behind Children and Return Decisions of Migrant Workers in China

This paper uses a dynamic survey data of China labor force to explore the impacts of child education on their parents’ return decisions by means of constructing an empirical model. The migration situation of children is the basis for us to distinguish the sample migrant workers. And those migrants who migrate with their children and those who leave their children behind in their hometowns are the two types of migrants among this model which we will analyze in urban areas. The results show that the probability for migrant workers in urban areas to return to hometowns will significantly increase when their children are left behind at home. While these parents tend to stay in the cities which they work and live in when their left-behind children enter the school age. The data we use is from the China Labor Force Dynamics Survey and we establish a model to analyze the effects of left-behind children. The empirical results show that the probability for migrants to return to their hometowns will decrease by 20.8 % when their left-behind children enter the school age. To a large extent, the emergence of such a huge contrast may be the result of the optimal decision-making of migrant workers. And the phenomenon of large-scale “migrant worker shortage” caused by such mechanism has intensified in the labor market of coastal cities. And most of these cities have implemented relevant stringent admission policies for migrant children to receive education in urban public schools and this break the intentions of the immigrant parents who plan to take the left-behind children to the cities to receive education in local schools. And these immigrants choose to return in the case of decline of the family net income.

Introduction
The transfer of a large proportion of rural workers engaged in the primary industry to secondary and tertiary industries in urban areas often contributes to the development of economic. In recent years, the number of migrant workers returning to their hometowns has experienced substantial growth. Throughout the world, return migration has been an integral issue in labor migration. In the 1990's, as the outflow of migrants increases, return migration also becomes noticeable. About one-third of all immigrants are estimated to return to their native homes (Murphy, 1999). And in some coastal cities of China, the phenomenon of labor force shortage has been gradually serious which has a great impact on social and economic development. Academic circles also pay considerable attention to this phenomenon. There are two opposing views concerned with return migration in Chinese policy circle. One considers return to be a negative factor because it exacerbates the problem of surplus labor in rural areas. The other considers return migration to be carriers of capital, technology, and entrepreneurship, factories that will contribute to the development of their native communities. Opinions are related to the perceived circumstances leading to the migrant's return. The literature offers several explanations for return migration (Stark, 1996). First, a migrant fails to find a good paying job elsewhere. Second, the returns to the human or financial capital accumulated in the destination areas are higher at home. Third, the cost of living is lower at home than in the destination areas. Hare (1999) examined the duration of the migration spell in a county in Henan Province with a representative survey data sufficient of migrant family information conducted in 1995 but she found very few permanent returnees. Murphy (1999) described the local government policies designed to attract migrants back to two counties in Southern Jiangxi Province and examined the potential contributions that returnees make to economic diversification. Ma (2001) used a sample of returnees collected in 1997 and finds a significant effect of urban employment duration on nonfarm employment upon return.
The Chinese Labor Force Dynamics Survey (CLDS) data can attribute to the representative results of analyzing return migration. The dynamic data has sufficient economic and non-economic data for family members. With the popularity of the theory of new migration economy, family form migration has attracted widespread attention in the academic community. When family factors are taken into consideration, children may play important roles in migrant families and affect their parents' return decisions. Dustman (2003) applied a panel data set with over 14 years old sample immigrants to a model whose parents have paternalistic preferences. The results of the model shows that children influenced return plans of family and there were differences in the effects of female and male offspring. And child education plays an important role in human capital investment for families and the significance of educational investment rises increasingly as parents are concerned with development prospects for children and return decisions. Several studies that draw on data from some developed counties find that if returns to educational investment undertake in the host county, are higher in the host than in the home country, and if the parent believes that the child's return probability increases in his town, educational investments should increase with the permanent migration probability, as should the child's permanent earnings (Dustman, 2007). When we combined the situation of left-behind children in rural areas with the reality of the Chinese society, we can see that left-behind children are facing rigorous difficulties and education problems. Left-behind children have lower performance in academic performance and psychology than those children accompanied by their parents (Antman, 2011(Antman, , 2012Wu & Zhang, 2017). On the one hand, immigrant parents are inclined to take their children to the cities to receive education as the cities can provide better job opportunities, earnings and other resources that rural areas couldn't offer. While most cities implement policies to control the permanent population to reduce the burden of migrant population, and the educational enrollment requirements for migrant children emphasized in the policies will have a great negative impact on this decision if the left-behind children migrate with their parents to the cities to be migrant children. Zhao and Shi (2017) believed that the educational dilemma of migrant children is an obstacle to the investment of human capital in the process of migration. Left-behind children are an important manifestation of it. Urban governments setting the high enrollment thresholds for immigrant children may lead the parents to choose to send the children to migrant schools or send them back to attend local schools in their hometowns when the children enter the compulsory education age. However, some studies find that there is a sizable quality gap between migrant schools and public schools or even with rural schools (Song et al., 2010;Lai et al., 2014). Then the aforementioned decision of the immigrant parents will be worth discussion. And Sun (2015) studied the survey data and found that family-level factors play important roles in affecting the return of immigrants. Many literatures provide evidence that migration choices of immigrants are influenced by the educational performance of their children (Liu et al., 2010;Nechyba & Strauss, 1998;Bayer, 2000). On the other hand, as the parents pay more and more attention to family human capital investment and child living conditions, the difficulties of study and life which the left-behind children in rural areas face are gradually attracting attention of society due to the lack of parents' care in the long term. Sylvie and Xu (2011) constructed complementary empirical models and applied a household survey data carried out in Wuwei County (Anhui province, China) to verify the impact of left-behind children on return migration of immigrants. They found that the left-behind children play an important role in pulling force which drives the migrant workers choosing return and the effect being stronger for pre-school children. Then, does the situation that left-behind children are going to enter the compulsory education age affect the return decision of migrant workers? Therefore, our first purpose is to examine to what extent the left-behind children in rural areas entering the compulsory education age would affect the return decisions of migrants.
In recent years, some negative effects of the growth of labor force in cities have attracted enough attention of the society and the urban governments began to introduce some policies to control the permanent resident population to ease the burden of public services. And among these policies, there are stringent educational admission policies to stipulate the important requirements for migrant children to receive education in urban public schools. And to some extent, these requirements are too difficult to meet for most of the migrant families. In that case, migrant workers will choose to return for the education of children and making up for the lack care of left-behind children. Then, the second purpose of this paper is to ascertain whether the return willingness of migrant workers will increase when the enrollment thresholds of children set by the stringent admission policies introduced by local governments are strengthened.
This paper constructs an empirical model by means of using the data from CLDS. When left-behind children in rural areas are going to enter the compulsory education age to face the difficult growing and educational situation, the return probability of immigrant parents who leave their children behind in their hometowns will be lower than that of migrants who migrate with their children. And for families with one child, the difficult ijef.ccsenet.org International Journal of Economics and Finance Vol. 10, No. 6;2018 growing and educational situation being faced by left-behind children will decrease the return probability of their migrant parents by 26.1%. However, this difficult growing and educational situation has no effect on the return decisions of those immigrants who migrate with their children. We also study the effect of such situation on the return decisions of those immigrants who live in cities that issue relevant stringent policies to set high enrollment thresholds for migrant children to receive education in urban public schools. The results show that those immigrants will be inclined to return to their hometowns if the governments of these cities have published relevant stringent education admission policies. We also do the robustness tests by controlling the sample and get the consistent results.
This article has the following innovations. First, this paper constructs a model which analyzes how the difficult growing and educational situations being faced by left-behind children influence the return decisions of their immigrant parents. Second, based on the results of previous studies, these immigrants who migrate with their children have a high urban adscription and are reluctant to return to their hometowns (Li, 2010;Wang & Zhang, 2017). However, we find that the return decisions of those immigrant parents who migrate with their children are more likely to be influenced by the changes of household net income. Third, the education admission policies issued by the urban governments which strengthen the enrollment restrictions for migrant children to receive education in urban public schools will increase the return probability of immigrants. Theoretically, these innovative researches can enrich the research on migration and return migration of labor force, and lay the foundation for future research. We also recognize that there are two possible endogenous problems. One is that the year in which the children were born will interfere the year in which they reach the compulsory education period, and the unobservable factors may influence the return decisions of immigrants and estimation bias are thus produced. So, we control the sample to limit the children born before and around September and then use regression discontinuity-difference in difference for analysis. The other is that we control the sample period to the situation that the immigrants have moved into the cities before the education reformation policies have been published. And this method will help us avoid the reverse selection problems of policy issuance. In the practical sense, taking full account of the reality of the Chinese social labor market and achieving the effective results by combining the empirical model can be beneficial to the process of decision-making for the relevant departments.
The remainder of this paper is structured as follows. Section 2 introduces the estimation method using representative China data. Section 3 describes the data and variables, and empirically examines how the difficult growing and educational situations being faced by the left-behind children when they enter the compulsory education age affect the return decisions of their parents, and measures to what extent the issuance of stringent education admission policies will affect the return probability of these immigrants. Section 4 discusses the heterogeneity that may affect the results and performs robustness tests. Section 5 concludes.

Method
In this section, we will discuss the impact of children on the return decisions of immigrant parents through different dimensions and conduct further analysis through the classification of number of sample children.

Families with No More than One Child
We first analyze the sample immigrants whose families have no more than one child. We then construct a probit model to measure the return probability: where return i equals 1 if respondent i chooses to return to his/her hometown and equals 0 otherwise, child i takes a value of 1 if the family of respondent i has one child and takes a value of 0 otherwise, left i is a dummy variable which represents the child of respondent i is left behind at hometown if it equals 1 and the child migrates with parents if it equals 0, and schage i is an age identification variable that is equal to 1 if the child of respondent i is 4 or 5 years old in the survey data of 2012 and will be entering the compulsory education age period in the same data of 2014 to confront the difficult growing and educational situations and equals 0 otherwise.
Meanwhile, X i means the personal characteristics variables of individual i and spouse and these variables will influence the return willingness of immigrant parents. Specifically, these variables include the child gender, the characteristics of respondent i (e.g., gender, nationality, registered residence, age, years of schooling, duration of floating, having medical insurance, family income, and marital status), and the characteristics of the spouse (e.g., nationality, registration residence, years of schooling, and whether or not she/he migrates with individual i). p j , l k , ijef.ccsenet.org International Journal of Economics and Finance Vol. 10, No. 6;2018 and c f represent the registration residence province of the respondent, the range of migration (inter-provincial, cross-city, and cross-county), and the dummy variables which represent the cities where respondent i migrates to, respectively. Ɛ i is the disturbance term.

Families with Only One Child
For those families whose number of children is only one, child i is equal to 1, so the estimation equation changes as: We focus on the two states of child migration on this sample which are being left behind at hometown or migrating with parents. What we are mainly concerned with is the estimated coefficient of , which indicates the effect of the left-behind children's difficult growing and educational situation on the return probability of immigrant parents when these children enter the compulsory education age (relative to those immigrants who migrate with their children to the cities). The definitions of variables in this model are the same as formula (1).

Effect of Stringent Education Admission Policies for Migrant Children on Return Decisions of Migrant Parents
In our sample, we can obtain the information that some cities have implemented stringent education admission policies for migrant children during the research. The urban governments introduced laws and regulations to strengthen the enrollment thresholds of public schools for migrant children to control the permanent resident population. These policies will affect the return decisions of migrants if they have the willingness to take the left-behind children to these cities to receive education in urban public schools. We then generate a policy identification variable and apply it to the sample which has no more than one child, then the estimation formula can be written as follows: While when we apply it to the sample whose family only has one child, then the formula changes as: ( = 1| ) = 0 + 4 + 5 + * + 9 + 10 * + 11 * + * * + + + + + where policy i is an identification variable that takes a value of 1 if the city where immigrant i live in has introduced stringent education admission policies to strengthen the enrollment thresholds for migrant children.
And this variable is equal to 0 otherwise. The other variables have the similar definitions with those in the aforementioned equations. What we focus on is the coefficients of and in estimation formula (3) and (4) which represent the influence mechanism of the relevant stringent admission policies in cities respondent i lives.
Considering the sample size and that there are some effects that are difficult to quantify, and these effects will influence each other in the samples whose families have multiple children. Therefore, this article does not analyze these family samples with multiple children.

Results
In this part, we will first analyze the survey data used in our empirical model and perform some relevant elaborations. Then, this paper will make an exhaustive analysis of the empirical results obtained by the model.

Data Analysis
The data of this article is CLDS2012 and CLDS2014. CLDS is a nationwide tracking survey data which was conducted by Sun Yat-sen University and focuses on the present situation of labor force in China. This large-scale dataset interviews respondents in 29 provinces and municipality cities except Hong Kong, Macau, Taiwan, Tibet, and Hainan. And these respondents are family members aged from 15 to 65 years among the sample families. As the floating population is the research groups, we control the sample respondents to be immigrants and drop those samples whose respondents have joined the army or have been remarried, divorced, or widowed. Then we obtain a sample which has 904 respondents who have at most one child aged from 0 to 16 and a sample which has 516 respondents who have only one child aged from 0 to 16 in the family. We apply interviewing willingness approaches to identify those migrants who choose to return to hometowns before and after their children reach the compulsory education period.
ijef.ccsenet.org International Journal of Economics and Finance Vol. 10, No. 6;2018 Specifically, these immigrants exist in the sample of CLDS2012, should have responded "more likely to return to hometown" or "very likely to return to hometown" when asked about their recent intentions of return migration, and should not be tracked in the sample of CLDS2014.
In 1980, China implemented the compulsory education law which requires children to enter schools upon reaching the age of six years. We define these children who face the difficult growing and educational situation in rural areas as those who are 4 or 5 years old during CLDS2012 because these children would have been aged 6 years by the time of CLDS2014. That is to say, these children don't enter the compulsory education period during the time of CLDS2012 and have already been facing difficult growing and educational situation in CLDS2014. If a child is left behind in his/her hometown, we classify the child as a left-behind child. Considering the registration time of the new school year, we restrict the policy promulgation time from January 1, 2012 to August 31, 2014 for the policy identification dummy variable. And we also control those variables which may influence the return decisions of immigrant parents. These control variables cover the individual and migration characteristics of the respondents, their spouses, and their children.  Table 1 shows the statistical results for sample families whose number of children is at most one. Columns (1) and (2)

Effect of Left-Behind Children's Difficult Growing and Educational Situation on the Return Decisions of Immigrant Parents
(1) Families with no more than one child First, we analyze these sample families whose number of children is no more than one. We also include the sample families without children in analysis to compare the effect of having children or not on the return decisions of immigrants. The equation (1) which constructs the probit model is used to analyze the effects. The coefficient β in equation (1)  their hometowns (relative to those immigrants who migrate with their children to the cities). The negative coefficient represents that the situation that the child is going to enter the compulsory education age drives the migrant parents more reluctant to return to their hometowns. Considering the cross-sectional correlation in the sample, the standard error has been clustered at the city level. The results and the coefficients which are reported in Table 2 have been adjusted to the average partial effect. Table 2 reports the estimation results of sample families whose number of children is no more than one (columns (1) and (2)) and whose number of children is only one (columns (3) and (4)). First, column (1) reports that the return probability of immigrant parents will increase by 15.5% if there is a child who is left behind at their hometowns, and the coefficient is significant at the 5% level. Meanwhile, compared with the migrant patents that leave their children behind at hometown, the return probability of these migrants who migrates with their child will decrease by 13%. That is, the left-behind child to some extent increases the psychological costs of immigrant parents, while the costs are smaller if they choose to migrate with their child. Previous studies find the consistent results (Wang & Zhang, 2017).
Second, we analyze the return decisions of these immigrants who migrate with their children and those who leave their children behind at their hometowns when their children are going to enter the compulsory education period and face the difficult growing and educational situation. The estimated results are reported in column (2) of Table 2. The return probability for immigrants who leave the children behind at the hometowns will be 20.8% lower than those who migrate with their children to the cities when their children are going to enter the compulsory education age and face the difficult growing and educational situations. The estimated coefficient is significant at the 10% level. These immigrant parents choose to stay in the cities as the net income of them to return to the hometowns will decrease because of the high expenditure of child education and the less labor opportunities and remuneration in the hometowns. Moreover, in order to provide their children with better living standards and educational conditions, staying in cities to earn more reward or take the child to the cities to receive education are the more preferred choices for migrant parents.
(2) Families with only one child When we discuss the effects of household samples with only one child, the results were also significant. Column (3) lists the results for those sample families whose number of children is only one. The return probability will increase by 13.7% if those immigrants leave their child behind at their hometowns, and the estimated coefficient is significant at the 5% level. And for these sample families that the immigrants leave their child behind at their hometowns, they have a 26.1% (significant at the 10% level) chance to stay in the cities if their children are going to enter the compulsory education period and face the difficult growing and educational situations. And the estimated results in column (4) are consistent with those results in column (2). These findings are also consistent with the previous studies (Sylvie & Xu, 2011). The mean partial effect is represented by the estimated coefficients in the table and the standard error which is enclosed in parentheses has been clustered at the city level. Respondent's personal characteristics encompass gender, nationality, nature of household registration, age, years of education, duration of migration of the respondent, urban medical insurance, and monthly household income. Personal characteristics of spouse cover nationality, nature of household registration, years of education, and whether migrate with the respondent. Respondent's household registration province indicates the dummy variables of 29 provinces. The range of migration represents interprovincial mobility, cross-city mobility, and cross-county mobility these three indicators. The city represents the dummy variables of city which respondent flows to. The estimated results using sample families with at most one child are presented in columns (1) and (2), while the findings using sample families with only one child are presented in columns (3) and (4). ***, **, and * indicate significance at the 1%, 5% and 10% levels, respectively.

Effect of Education Admission Policies Enhancing the Enrollment Thresholds for Children
A series of problems for city immigrants increasingly attract the attention of the governments. And some governments have implemented relevant policies to strengthen the management of household registration for immigrants which are designed to control permanent resident population to reduce the burden of the city. These promulgated policies stipulate that migrant children receiving education in urban public schools requiring "three certificates", some more stringent needs the residence permit and meet the required length of residence in the city on the basis of "three certificates". These policies to a large extent raise the thresholds for migrant children to receive education in local urban public schools. And those stringent requirements are too difficult for most migrant families to meet. The entry of compulsory education age for children will place the migrant parents in a dilemma. Then the effect of children's difficult growing and educational situations on the return decisions of migrants will differ if parents have the willingness to take the school aged left-behind children to the cities to receive education. To study the effects, we use a policy dummy variable to identify whether the city the respondent lives in has introduced stringent child education admission policies during the period from January 1, 2012 to August 31, 2014. The dummy variable in the model which we construct is po i , which takes values of 1 and 0 to represent having introduced stringent policies and not, respectively. We analyze the impact of these policies by using the probit model constructed by equations (3) and (4). The coefficients to be focused are δ and η, which illustrate the effect of child's difficult growing and educational situation and entry into school age on the return decisions of immigrant parents who live in cities that have published stringent admission policies. The standard errors have been clustered at the city level. Note. The regression results using two samples whose families have at most one child and only one child respectively are presented in the table. The mean partial effect is presented by the estimated coefficients and the standard errors which are enclosed in parentheses have been clustered at the city level. Respondent's personal characteristics encompass gender, nationality, nature of household registration, age, years of education, duration of migration of the respondent, urban medical insurance, and monthly household income. Personal characteristics of spouse cover nationality, nature of household registration, years of education, and whether migrate with the respondent. Respondent's household registration province indicates the dummy variables of 29 provinces. The range of migration represents interprovincial mobility, cross-city mobility, and cross-county mobility these three indicators. The city represents the dummy variables of city which respondent flows to. The estimated results using sample families with at most one child are presented in columns (1), while the findings using sample families with only one child are presented in columns (2). ***, **, and * indicate significance at the 1%, 5% and 10% levels, respectively.
The regression results are reported in Table 4, and the estimated coefficients illustrate the mean partial effect. Column (1) describes the results of those sample families whose number of children is at most one. The coefficient δ in the probit model is positive and represents that the immigrant parents are more inclined to return to their hometowns if they live in these cities that have published relevant stringent education admission policies ijef.ccsenet.org International Journal of Economics and Finance Vol. 10, No. 6;2018 and have a better level of development in economics. This result represents that cities introducing relevant stringent education admission policies will increase the return probability of immigrants by 52.9% under the circumstance that children are going to enter the compulsory education age and face the difficult growing and educational situation. Also, column (2) reports the regression results using sample families with only one child. And the estimated coefficient η is positive and is significant at 5% level, which represents that the immigrant parents who live in cities with implemented stringent education admission policies have 69.1 percentage points higher return probability than that of immigrant parents who live in those cities without implemented relevant stringent policies. The estimated results in this column are consistent with those in column (1).

Discussion
Based on the above studies of this paper, we further discuss and analyze the possible heterogeneity that may lead to biased results in the sample. In this part, we use the probit regression to perform some robustness tests. In particular, we will examine whether its heterogeneity affects the estimation results by controlling the sample even further.

Gender Heterogeneity of Sample Respondents
Reviewing the changes of migration patterns, starting with a single parent migration followed by parental migration and migration of entire family, we can obtain the changes of migration decisions in a family. Generally speaking, the father works as a pillar of the family and he has the right to make decision for the whole family. To examine whether gender heterogeneity affect the regression results, we control the sample to male respondents. The mean partial effect is presented by the estimated coefficients and the standard errors which are enclosed in parentheses have been clustered at the city level. Respondent's personal characteristics encompass gender, nationality, nature of household registration, age, years of education, duration of migration of the respondent, urban medical insurance, and monthly household income. Personal characteristics of spouse cover nationality, nature of household registration, years of education, and whether migrate with the respondent. We control the sample by dropping female respondents. Respondent's household registration province indicates the dummy variables of 29 provinces. The range of migration represents interprovincial mobility, cross-city mobility, and cross-county mobility these three indicators. The city represents the dummy variables of city which respondent flows to. ***, **, and * indicate significance at the 1%, 5% and 10% levels, respectively.
We use the probit model defined by equations (1) and (2) to analyze the regression effect. The results are reported in Table 4. The estimated coefficients have been converted to average partial effects, and the standard errors have been clustered at the city level. The estimated results for those families whose number of children is at most one are reported in column (1). The regression coefficient of β is -0.458 and is significant at the 1% level. This reveals that the return probability of the migrant fathers who leave the children behind at hometowns will decrease by 45.8 percentage points compared to those migrant fathers who migrate with their children when the children enter the compulsory education age and face the difficult growing and educational situation. This value is more than double than that of the coefficient in Table 2 (20.8 percentage points). The regression results using sample families with only one child are reported in column (2). The coefficient of β is -0.501 and is significant at the 1% level. This figure is also almost double of the coefficient in

The Migration Distance Heterogeneity
In terms of migration trend and economic development status in China, provincial cities and eastern coastal cities develop better than other cities and these fast developing cities can provide these immigrants more job opportunities and public services that other cities couldn't offer. So that most of the immigrants who come from less developed areas in central and western China tend to migrate to the provincial capital cities and eastern developed cities in recent years. While migration range in our sample includes three forms which are inter-county, inter-city, and inter-provincial. And the latter two kinds should be mainstream choices according to above analysis. Then we can reasonably presume that choosing close distance migration can create convenience for the immigrants to work in local areas and take care of their families simultaneously, reduce the risk of loss, and prepare for the whole family migration if necessary. The effect of this migration form will differ from that of other two forms on the return decisions of immigrants. So we examine whether the migration distance heterogeneity affect the regression results by excluding inter-county migration from our sample. The mean partial effect is presented by the estimated coefficients and the standard errors which are enclosed in parentheses have been clustered at the city level. Respondent's personal characteristics encompass gender, nationality, nature of household registration, age, years of education, duration of migration of the respondent, urban medical insurance, and monthly household income. Personal characteristics of spouse cover nationality, nature of household registration, years of education, and whether migrate with the respondent. Respondent's household registration province indicates the dummy variables of 29 provinces. The range of migration represents interprovincial mobility and cross-city mobility these three indicators. We exclude those inter-county migration respondent samples. The city represents the dummy variables of city which respondent flows to. ***, **, and * indicate significance at the 1%, 5%, and 10% levels, respectively.
The regression results that use CLDS data which has excluded inter-county migration samples are reported in Table 5. The estimated results for families with at most one child and only one child are reported in columns (1) and (2), respectively. The estimated coefficients have been converted to average partial effects, and the standard errors have been clustered at the city level. These immigrant parents in the sample families with at most one child have a 32.4% probability to stay at the cities when the left-behind child enters the compulsory education age and faces the difficult growing and educational situation. The coefficient value of β is more than half of that in Table 2 (20.8%). Column (2) in Table 6 lists the regression results for those sample families whose number of children is only one. The estimated coefficient β is -0.321 and is significant at the 5% level. The result indicates that the return probability of immigrant parents who leave their children at hometowns will be 32.1 percentage points lower than that of the immigrants who migrate with their children together if the children enter the compulsory education age and face the difficult growing and educational situation. We use the sample data that exclude those families with inter-county immigrants to identify the actual return of immigrant parents, and the estimated results are consistent with the aforementioned conclusions.
Comprehensively speaking, the results of the above empirical study are sufficient for the study of the migrant families with at most one child and with only one child in this paper. However, for sample families with multiple children, considering the complex cross effects between the children and the statistical errors in the sample, the research of multiple children sample is scarce in our article which is also an important part to be strengthened in the future research.

Conclusion
China has at least 13.95 million migrant children and 17.26 million left-behind children in 2016 according to the data released by the Ministry of Education. In recent years, China has witnessed a wide gap between the supply and demand of future labor market. And when the left-behind children enter the compulsory education age, immigrant parents are inclined to stay in the cities and take their children to the cities to receive education in urban public schools with their whole family because these left-behind children are faced of a series of education problems and difficult situations that are thorny to overcome to some extent. While the inflow of a large number of migrant population aggravate the burdens of the cities, then some of the cities implement some reformation policies to control the permanent resident population of the cities. And the stringent admission stipulation for migrant children to receive education in urban public schools is an important part of these regulations which are incapable to meet for most migrant worker families. So the immigrants will choose to return to their hometowns as the net income of the family decreases. We can understand the return effect, its mechanism, and why some cities are faced with labor force supply shortage by analyzing this problem. We use the data from the CLDS to validate the model and analyze the effect.
This paper presents two valuable findings. One is that the return probability of immigrant parents who have only one child will decrease by 26.1% if their left-behind child is going to enter the compulsory education age and face the education problems and difficult situations. The other is that we sort the cities to distinguish whether have introduced the stringent education admission policies or not and find that those immigrant parents who live in cities with published stringent polices for migrant children have 52.9 to 69.1 percentage points higher probability to return to their hometowns compared with those immigrants who live in cities without relevant published stringent policies. We also control the sample to drop out the female sample and inter-county migration samples and find that the probability of return migration will decrease by 32.1 to 50.1 percentage points when the left-behind child is going to enter the school age. In general, education problems and difficult situations of left-behind children and the unfair enrollment thresholds set by the stringent education admission policies can attribute to the shortage of labor and the return of immigrants.
Figuring out the driving force of immigrants' return migration and the effect of the stringent enrollment thresholds on this analysis has representative meanings. Solving the education problems and difficult situations of left-behind children can help the immigrants reduce the family worries. While the stringent education admission policies exclude the migrant children from the urban public schools educational system. And if these immigrant parents could take the left-behind children to the cities that have introduced reformation policies and properly solve the problem of migrant children to receive education in local public schools, then, the shortage of labor force in these cities will ease. Therefore, to promote the education reformation policies to reasonably set admission requirements for migrant children to receive education in urban public schools and to address a series of educational and living problems of left-behind children, local governments still have much to improve. Specially, the government should further deepen its current reformation for the floating population to accept the migrant workers to send their children to public schools in urban areas and the hometown governments should vigorously develop the industry and introduce relevant welfare policies to attract migrant workers to return for employment. The reformation policies will be beneficial to the equal provision of education for all children, address the shortages in the urban labor force. Also, the development of their hometowns will accelerate urbanization and help them take care of their children and families.


EVOLUTION AND CONTEMPORARY TRENDS OF THE INTERNATIONAL MONETARY SYSTEM

The growth dynamics of international exchange and capital flows is conditioned by the efficiency of the international monetary system whose basic task is to provide for international liquidity and smooth international payments. The tendencies in international economic relations in the time of globalisation have determined further directions for the development of the international monetary system. The breakup of the Bretton-Woods System initiated the establishment of a new European monetary system with the aim to stabilise the exchange rates and improve further process of integration and international economic relations. In this research paper we have pointed out to the fact that economic interdependence of souvereign countries leads to coordination of macroeconomic policies, and that it can motivate monetary integration within the monetary policy. The objective of this research paper is to emphasize the stability of the international monetary system as a prerequisite for sustainable growth of national economies and monetary union. The contemporary international monetary system is characterised by the trend of reduced number of national currencies, as this is a logical conseqence of increasing European integrations, but also beacuase of significant economic advanatages. Simultaneously, the costs of the euro changeover and introduction of a common currency are lower if economic performances of member countries mutualy converge.

INTRODUCTION
Efficient international monetary system and stable monetary medium which would function as international means of payment, international monetary reserves and clearing means of payment in international transactions destinguishes itself as a prerequisite for the development of international trade and capital flows. Contemporary international monetary systems reflect complex economic and socio-political relation and as such should be observed from various aspects.
Evolution of contemporary international monetary system has started on the principles and systems of the gold standard. The backbone of the gold standard was defining the value of a national currency by a stated quantity of gold and its unrestricted convertibility into gold. By fixing a currency price to gold, the gold standard aimed to restrict the monetary increase in the world economy providing thus stability of the world price level. The first organised forms of international monetary systems were therefore based on the gold standard system. Discovery of big gold deposits in the middle of XIX century led to the establishment of gold value as a system of monetary organisation throughout the world. Successful functioning of the gold standard colided with the transfer to liberal stage of capitalism in which conditions for its automatism in regulation of international monetary relations were met. At that time Great Britain was the leading economic power in international trade and was simultaneously developing its financial institutions, which made it become the center of international monetary system.
Increase of the USA role in the world economy as well as tendencies in international economic relations in globalisation have determined further directions for the establishment and development of international foreign currency and monetary system. Goals of countries' internal policies after the period of the gold standard have been gaining on importance, and attempts to reestablish the gold standard have resulted in creation of different systems of fixed exchange rates. The end of the World War II was also the beginning of reforms of the international monetory system which endevaoured to reconcile the goals of internal and external equilibrium. Having learned from the consequences of the World War II, the allies started to propose a new changed form of the international monetary system, the result of which was the establishment of the Bretton-Woods international monetary system. Due to changes in international economic relations in the end of the 1960s, the establishment of the new world monetary and exchange rate system was initiated. The European Monetary System was established with the goal to stabilise the exchange rates, improve further integration process and contribute to stabilisation in international economic relations. The European Monetary System delivered satisfying results, as it provided for convergence, decrease in inflation rate and exchange rates stability. Monetary stability and discipline imposed by the System led to price stability, which was the goal of monetary policy even in the countries with relatively high inflation rates. The success of the System initially created to protect Europe from international exchange rate disturbancies accounted for the establishment of the monetary union as the consequent step. Being the highest stage of the European integration, the monetary union could succeed only with the economic convergence of its member countries. This paper demonstrates that economic interdependence of souvereign countries leads to coordination of macroeconomic policies, which within the monetary policy can be motivation for monetary integration. This derives from the fact that introduction of a common curency has significant economic advantages-lower transaction costs, higher price transparency and monetary stability. Simultaneously, the costs of the euro changeover and introduction of a common currency are lower if the economic performances of member countries mutualy converge. The member countries' convergence from the aspect of the currency criteria shows that values and levels of inflation rate, height of interest rates on government bonds and exchange rate mechanism were a prerequisite for the establishment of the union and an indicator of stable movements in the contemporary monetary system. However, escalation of the global crisis led to great market oscillations, instability and assymetric shocks in various countries.

CHARACTERISTICS AND DEVELOPMENT OF THE INTERNATIONAL MONETARY SYSTEM
In the period before the World War I the world economy was based on the gold standard, which was a guarantor of printing paper money with gold coverage and which implied direct gold convertability for the majority of currencies. "Linking currencies' value directly to gold caused the establishment of an international financial system with a fixed exchange rate between currencies. ''A significant advantage of the fixed exchange rate according to the gold standard was in stimulating the world trade, as the fixed exchange rate eliminated uncertainity as part of the fluctuating exchange rate." (Мishkin 2006). The gold standard implied the following basic rules necessary for its regular functioning and respect by the countries which accepted it: -monetary authorities of each country had to determine the fixed value of the national currency in gold; -there was free import and export of gold; -there was possibility of automatic money supply fluctuation depending on the gold status and movements and -there was sufficient prices and wages flexibility.
The fact that the monetary authorities of the respective countries respected the regulations enabling the functioning of the gold rule provided for automatic equilibrium between balance of payments and world prices.
During the gold standard the main responsibility of the central bank was securing the official parity between its own currency and gold; for the maintenance of this price, the central bank needed adequate gold reserves. Creators of the policy have thus considered the external equilibrium not in the context of the aimed current account status, but as a sitution in which the central bank neither acquired some gold from abroad nor ( which is more important) lost it too fast in relations with other countries (Krugman and Obstfeld 2009).
Nevertheless, the flow of gold between the countries changed with time, which simultaneously led to frequent oscilations of the money amount and prices, and pointed to the fact that by respecting the gold standard a country had no control over its monetary policy, as the money amount depended on the flow of gold between countries. The focus was on external goals, i.e., putting the world economic stability ahead of internal stability and economic policy. This makes us conclude that the gold standard was the first form of transfer of the monetary souvereignty of one national economy and weakening of the central banks' discretion right in conducting monetary policy.
The First World War marked the end of the gold standard, as due to recession and great market disturbances countries were not any longer capable of converting their currencies in gold. International liquidity became a more frequent issue because of continuous fear that the world monetary gold reserves were not sufficient to provide for smooth international payments. The war and great expenditures for its financing, and thereafter for the recovery of the war-torn economies, great economic crisis and economic policies with the focus on full employment significantly changed circumstences in which the international monetary system was functioning. Many countries were considering options between external and internal equilibrium, which led to monetary desintegration at the beginning of the 1930s.

Bretton-Woods international monetary system
The increase of the USA role in the world economy and the establishment of new international relations have determined directions of the establishment and development of the new monetary system. After the period of gold standard, the goals of countries' internal policies were becoming increasingly important, and attempts to reintroduce the gold standard resulted in formation of different systems of fixed exchange rates. Just before the end of WWII, the allies started suggesting a new form of interanational monetary system. Although there were four plans suggested for the organisation of international monetary cooperation, White's Plan was chosen to be the basis for the establishment of an international financial organisations. The Plan was based on the main principles of the agreement signed by 35 out of total 44 countries present at the conference in the American city Bretton Woods in 1945.
White's Plan reflected the economic and political policy of the USA which was then economically stronger than the majority of countries, and with huge gold reserves. The Plan introduced by White recommended a kind of universal acceptance of the gold standard The new system was guided by the following principles: -monetary policies in the world can be adequately governed only with the full cooperation of all, and primarely of the main financial centers in the world and -international equilibrium cannot be established unless there is internal equilibrium and economic policy of each country has to be directed to the achievement of internal and external equilibrium.
Taking into account the fact that after the WW I the USA was the most powerful economy, the majority of international exchange transactions were conducted in dollars, and thus the basic characteristic of the Bretton-Woods system was the establishment of the fixed exchange rate based on the convertability of the US dollar in gold. Central banks were buying and selling dollars and were keeping them as exchange rates and through operations at the exchange market they were maintaining the exchange rate. The US dollar which was used also by other countries to nominate the funds kept as exchange reserves was granted the status of reserve currency (Мischin 2006).
When subjects abroad, primarely central banks, want to keep their exchange reserves in foreign currency , this means that the respective foreign currency has the status of the world reserve currency. The second important proof that one currency represents a world reserve currency is the fact that it is often used in international financial transactions. Today this is the role of the US dollar and euro. International status of dollar was established in Bretton Woods system (Кovačević 2014).
The International Monetary Fund and the International Bank for Reconstruction and Development were established on the basis of the Bretton-Woods agreement. The basic task of the International Monetary Fund was to promote the development of the world trade by establishing rules for the maintenance of the fixed exchange rate and by granting loans to countries facing difficulties in the balance of payments (crediting their deficit). Advancement of the international cooperation through consulting and joint problem solving of monetary issues, growth of the international trade, employment, income and production increase, stabilisation of exchange rates and prevention of competitive depreciation have been pointed out to as the basic functions of the Fund. Besides the aforementioned, some of more important functions of the IMF are multilateralism in international payments for current transactions and removal of exchange restrictions impeding the increase of the international trade, provision of financial funds for helping the member countries to balance their balance of payments and decrease imbalances. The task of the IMF is not only solving problems of respective countries, but the functioning of the international monetary system as a whole for the purpose of the establishment of the world growth. Being such, the Fund represents today an inevitable financial institutions influencing the main global financial flows.
The Fund's capital was formed in the way that all member countries paid in certain quotes based on their economic capacity taking into account the following: amount of national income, gold or dollar reserves, average import and its movements. At the beginning there were 30 member countries in the IMF and until today the number of the member countries has increased to 188. However, when the Bretton Woods system collapsed in 1971, the IMF was entitled to much wider power of attorney and new, more important roles it had initially.

European Monetary System
The modern world economy is characterised by the trend of decreasing number of national currencies,which is a logical consequence of increasing international economic and monetary integrations. Domestic currency makes important constituent of the country's sovereignty, with the possibility of exerting active influence on real economy. A stable and convertible national money unit is thus considered to be a realiable economic measure of value and success of the economic system, especially in monetary policy.
Economic as well as political factors have always been the basis for European integrations: from the desire to prevent wars and destructions to economic benefits of enhanced integrations and establishment of democratic society in the entire Europe. Due to changes in international economic relations in the end of the 1960s new impulses for the establishment of the new world monetary and exchange system arose. It was said that the main reason for this was that ''the sixties were the time of irresponsible inflatory monetary policy of the USA -which printed money for the financing of Vietnam War''. With regard to the fact that at that time all main currencies were pegged to dollar (through global system of fixed exchange rates, i.e. Bretton Woods system), American inflation was transferred to Europe. This resulted in gradual breakdown of global system of fixed exchange rates. Historically, European Monetary System served as a bridge between Bretton Woods system, the center of which was dollar, and monetary union'' (Baldwin and Wyplosz 2010).
Economic theory foresees that when reserve currency countries accelarate their monetary increase, as this was the case with the USA in the second half of the 1960s, one of the consequencies is automatic rise of the monetary increase and inflation abroad, with regard to the fact that the foreign central banks buy reserve currency in order to maintain their exchange rates and increase their own money supply during this process (Krugmann and Obsfeld 2009).
As response to decreased demand for American dollar and divergence priority of economic policies of the EEC member countries, modes for recovery of the intereuropean stability of exchange rates were sought for. In order to stabilise their own prices and restore the internal equilibrium, they had to abandon fixed exchange rates and let their currencies fluctuate.
In 1977 the European Commission suggested the establishment of the European Monetary System which was founded at the conference of presidents and prime ministars of the Nine in Bremen in June 1978, and which came into force on 13 March 1979. At that time members of the EMS were all EEC membe r countrie s: Ge rm any, France , Gre at Britain, Belgium , Ne the rlands, Luxem burg, Denmark, Ireland and Italy. The EMS was founded with the aim to provide for monetary cooperation and stability between the countries accelerating in this way the creation of common currency, monetary authority and monetary union in Europe and achieving higher level of economic integration. The European Community countries decided to establish stability system in Europe characterised by the lowest inflation rates, tighter economic cooperation between its member countries and prevention of negative effects of external economic shocks in form of too frequent dollar fluctuations. After the four-year adaptation of central exchange rates between member countries' currencies and alignment of economic policies, i.e. after 1983, better conditions for higher level of stability between the currency exchange rates in the EMS were created.
The European Monetary System is the most powerful instrument of monetary integration in Europe and creation of common economic and monetary union, with its explicit goals as follows: -exchange rate stabilisation through more intensive monetary cooperation between the EMS member countries, -adavancement of further integration process and -contribution to stabilisation in international economic relations.

EUROPEAN MONETARY UNION AS THE HIGHEST LEVEL OF MONETARY INTEGRATION
Generally speaking, the European Monetary System has delivered satisfying results, as during the 1980s it provided for convergence and decreased inflation rate with stability of the exchange rates. The European Monetary System was successful in securing monetary stability, whereas the discipline it imposed led to setting as objective the price stability in the countries with the relatively high inflation rates. This paved the way to higher European integration stage, as the economic convergence of the member countries is the basis for the establishment of economic and monetary union. Number of instabilities in the world monetary relations and disagreements between respective Union members regarding measures that should be undertaken towards the establishment of a common monetary union delayed the introduction of the common currency in Europe for 12 years. The establishment of the European Monetary Union underwent three stages, the first of which started in the 1990s. This first stage was characterised by the full liberalisation of capital with the aim to eliminate protectionism measures and restrictions of free capital movements. Simultaneously, the economic policies were coordinated, particularly monetary and fiscal policy, in accordance with the Maastricht convergence criteria. The second stage started on 01/01/1994 with the establishment of the European Monetary Institute with its headquarters in Frankfurt. The EMI is a predecessor to the European System of Central Banks whose headquarters is today in Frankfurt. During the second stage the national central banks still kept autonomy in implementation of the monetary policy (Lovrinović and Ivanov 2009). The third stage started by irrevocable fixation of exchange rates to euro and transfer of monetary sovereignty of the EMU member countries to the common central bank. The overall role of the monetary policy was taken by the European Central Bank in Frankfurt.
Creation of Monetary Union according to Maastrich Criteria implies meeting the monetary and fiscal convergence criteria in order to achieve optimal functioning and survival of the EMU. In this paper we will reflect on monetary criteria in order to emphasize the importance of stable and efficiant monetary system.

Monetary convergence criteria
One of the basic characteristics of the European unification in all the stages of the European history is heterogeneity of the countries which make up the Union. This heterogeneity reflects in socio-cultural specifities, history and level of the economic development. (Vukmirica and Špirić 2005). Exactly the similarities between the member countries, primarily regarding their economic development are considered to be a prerequisite for successful functioning of the monetary union. Nominal convergence implies fullfilment of the quantitively precised criteria on member country's readiness to enter the eurozone, as prescribed by the Maastricht Treaty.
A country is allowed to accede to the monetary union if it meets the required criteria of the monetary convergence (De Grauwe 2004) as follows: 1. its inflation rate is not higher than 1,5% in comparison to the average of the three lowest inflation rates of the member countries, 2. long-term interest rate on government bonds is higher than the average long-term interest rate in three member countries with the lowest inflation, 3. accepts exchange rate mechanism (ЕРМ II) of the European Monetary System, and if 2 years prior to its accession to the Union it does not execute its currency devalvation.

Inflation convergence
The primary objective of the European Central Bank was set with the establishment of the monetary union and transfer of monetary sovereignty of the member countries to supranational central bank, which contrary to the quantitative objectives, prioritised the quantitative, i.e. stabilising objective of the monetary policy. Contrary to the Anglo-French banking model, the German model of the Bundesbank, which was accepted for the formation of the European Central Bank, emphasises the stability of prices as the primary objective of the central bank. According to the analytical frame of the monetary integrations, monetary union between two countries implies the existence of the common central bank, whereas it is pointed out that formation of a monetary union with a country with high inflation reduces the prosperity of the country with a low inflation. This is likely to derive from the fact that the common central bank reflects the average preferences of the member countries causing thus increase in the inflation rate of the Union -benefits from the monetary union are lost, i.e. transaction costs and risks are lower (De Grauwе 2012). In order to attain the primary objective, i.e. meet the inflation convergence criterion with this anti-inflation process, the member countries faced an inevitable temporary increase in unemployment (according to movements along the short-term Philip's curve).
With the development and enlargement of the monetary union, besides already mentioned heterogeneity of the member countries, Europe has been facing unequal increase in (macro) economic indicators of the member countries, which under the crisis circumstances particularly highlights the conduct of the common monetary policy. During 2004 eight middle and eastern European countries and two Mediterranean countries became part of the European Union, and in 2007 Rumania and Bulgaria became its full members. Meeting the inflation convergence criterion within the nominal convergence criterion is an important step and demands effort from the new member countries on their way to monetary union. According to the data from the Table 2, general evaluation is that there is a visible trend of inflation rate increase in all new member countries in the period from 2003 to the beginning of the recent crisis, i.e. 2008. Inflation rates movements are result of the then global increase in food and energy prices, which was clearly reflected in the price increase of the consumer basket in these countries during the observed period. New member countries also recorded high salaries increase which is not sustainable in the long term, as it does not accompany the appropriate productivity increase. Since the process of accession to the developed EU countries implies also higher inflation rate (Balasca-Samuelson effect), they can be reduced by restrictive monetary and fiscal policy, which can result not only in lower increase and employment rates, but also in appreciations of the exchange rate. All this may lead to competition loss. A country can accede to the Union only if the inflation rate is not higher by 1.5% than the average of the three lowest inflation rates of the member countries.

Interest rate convergence
Long-term bond interest rate indicator represents a measure of continuity and sustainability of the country's convergence process, i.e.'' reflection of the financial market on evaluation of the economic sustainability of the member country'' particularly regarding stability of fiscal balance and risk premium. Interest rate convergence on long-term bonds is justified, as excessive differencies in interest rates prior to the accession to the Union may lead to great capital gains and losses when entering the EMU. This would cause great disturbances on national capital markets. But to be restricted, differences in interest rates have to be decreased before a country joins the EMU. On the other hand, the level of the interest rate is reflexion of investors' trust in country's finances and financial instruments and their inflatory expectations. The greater a member country's divergence from the fiscal convergence criterion, i.e. the farther the deficit from 3% GDP, the greater divergence between interest rates on member countries' government bonds (Akitoby and Stratman 2008).

Source: author's adaptation, adapted from Eurostat 2017
The Маastricht criterion specified permitted deviations of the long-term interest rates which in the EMU countries should not be higher than 2% from the average recorded in three countries with the lowest inflation (interest rate convergence criterion). The Table 3 displays negative convergence, i.e. divergence of interest rates on long-term government bonds during the crisis period. In 2010 there were significant differences as direct reflection of the most indebted member countries of the Union. Financial and economic crisis influenced rising need for financing the respective member countries of the Union and additional increase in indebtedness costs. Thus the increased difference in government bond yields signalled that investors were less motivated to lend money, which endangered this country's access to the international capital market and simultaneously increased indebtedness costs.
Market development urges creation of the government bonds yield curve. It contains reference values for yields on other bonds on the capital market. Difference in yield represents all differences between two countries or regions which influence bonds' offer and demand. These are e.g. political environment (political risks), expected returns, economic risks, expected inflation and expected exchange rate change, liquidity, mode of adapting respective country's bonds to most important investors' portfolio and similar. Spread changes, i.e. their rise, reflect increased concern of financial markets for capacity and capability of respective countries to face their debt in future (Žigman and Cota 2011).
Government bonds with fixed yields are the main pillar of the modern securities market. The curve (Figure 1) representing government bond yields is referent and serves as a guideline to future interest rate and inflation movements.
The yield span within the euro zone has had positive convergence since the Euro was introduced in 1999. Although there was a lesser spread widening at the beginning of 2000 due to dotcom bubble and terrorist attacks in September 2001. There was a pronounced convergence of yield on 10-year government bonds of the EMU member countries until 2007. After 2005 a moderate turn was noticed in Greece, Italy and Portugal in relation to the reference value. From the year 2007, the interest rate spread between German bonds and the remaining eurozone has been recording significant increase. This is also confirmed in the research made by Copeland and Jones (2001) who showed that differential appeared and expanded during crisis periods, as this was the case during the Russian crisis (1998), or currency crisis in Turkey (2001).

Source: Eurostat 2009
If the interest rates on government debt exceed the increase rate of the economy, the debt is set dynamically, which leads to ever increasing government debt and sustainability problem of the national economy. This causes negative cost and crisis spill-over, which has negative influence on the functioning of the monetary union.

INTERNATIONAL MONETARY SYSTEM IN THE PERIOD OF CRISIS
After ten years of relative stability and strenghtening of the euro as a common currency, the issue of the future of the euro and destabilisation of the European economic and monetary integration was raised particularly due to financial and debt crisis. The fact is that after the crisis the criteria have become indirectly tighter, accompanied by various new challenges and conditions and they have influenced further enlargement of the European monetary and economic integration as well as the entire international monetary system. Economic and political differences between the member countries of the monetary union constitute favorable grounds for the development of assymetric shocks. Shocks influencing different economies similarly are known as symmetric shocks, whereas those having various implications, or reflecting implications only to one country in a specific way are known as assymetric shocks. Negative implications of symmetric shocks are mitigated by methods of common economic policy, whereas the assymetric ones pose a problem for common currency area, as there are no measures of the local or regional monetary policy.
Financial sector and banks are the backbone of the functioning of the modern countries' economic systems, also of those within the Eurozone. The key issue of the recent crisis was in securing stability and solving accumulated problems of the mentioned sector. The crisis which broke out in 2008 with the breakdown of some of the biggest financial institutions led to necessity of the gove rnment financial aid to a gre at num be r of banks. This gove rnment aid was financed by indebtedness on financial markets, which resulted in drastic increase in budget deficit and public debt with the most developed core eurozone countries, and even more drastic one with other eurozone countries. The eurozone countries as Greece, Italy, Spain, Portugal, Ireland and other could take loans with favourable interest rates on the world financial markets even without fiscal discipline expected from them as the EMU member countries. This was enabled by the euro, as investors were ready to lend money even to countries with the bigger risk taking into account credibility and stability of this world currency. The abovementioned countries were referred to indebtedness even before the breakout of the crisis due to insufficient domestic accumulation (savings) for investments and need for faster economic development and competitiveness. Interest rates started to increase, and some of the aforementioned countries whose investments still had no results already recorded deficits in their balance of payments.
In the crisis spreading model according to which one country's banks are buying other country's bonds, the crisis can spread across borders also by banks. For example, if the banks in the fiscally insolvent countries have borrowed large amounts of money from banks from other countries, these banks will also encounter difficulties due to interbanking relations. But regardless of the problem spreading mode, difficulties always arise because countries, i.e. governments, which due to fiscal capacity are in normal times considered to be first-class debtors and ultimately '' savers'' do not have financial capacity to guarantee for their stabilisation function. Mitigation of the crisis effects and increased control mechanism are pointed out to be the primary objective of measures and models of political instruments in order to avoid such big crisis in future or to at least alleviate their consequences. Seriousness and duration of the crisis forced the EU countries and their governments to adopt numerous measures and programms for countering negative effects of the crisis, supporting thus the key sectors of economy. The response of the countries' governments in the period of crisis and after crisis has important implications for the maintenance and functioning of the international monetary system.

Тable 4. Identified problems within the EMU
The first consequences of the world financial crisis were illiquidity and losses due to devaluation of the property under the mortgage-backed securities and their financial derivates. Recovery of the financial market liquidity was therefore the first measure to be undertaken. Decisions of the central banks on securing liquidity as well as the measure undertaken by the majority of the countries' governments and parlaments to give guarantees to the financial sector proved to be efficient in preventing the breakdown of the global financial system.
Uncertainty regarding fiscal insolvency of the member countries initiated the second crisis wave in Europe. There was rising fear from countries' insolvency crisis accompanying the banking crisis. Competition losses and vulnarable banking sector endangered the countries' solvency and questioned the sustainability of the public finances. Continuous deficit increase and huge public debt reached their peak during 2011. The eurozone debt crisis led to new financial disturbances on the market, loss of trust among market participants and finally to recession in Europe. Due to fiscal restrictions in implementation of the common crisis management, the EMU did not have redistribution mechanism and instruments to help its member countries, and thus other solutions were produced. Unrealised similarities among member countries' economies make the common monetary policy inadequate and less efficient for stronger as well as for weaker economies challenging thus the sustainability of the monetary union foundation.
On the basis of the aformentioned it is obvious that the member countries have attained different level of convergence and economic growth, and that it is justified to raise the issue of their implication to the economic situation within the monetary union. Doubts regarding sustainability of the economic and monetary union are not new, but they are gaining on intensity and importance only under crisis circumstances and market instabilities when assymetric shocks are pronounced.

Role of the Internation Monetary Fund during financial crisis
The bre akout of the recent financial crisis rose nume rous issue s re garding the role and participation of the Internataional Monetary Fund in the world financial flows, emphasising thus the necessity of powerful and timely response of this institution.
In order to meet the ever increasing financial needs of the crisis-stricken countries and to strenghten the global economic and financial stability, The International Monetary Fund has significantly increased its lending capacities during the financial crisis. Through advancement of the lending system and its increased volume, it offered to countries solutions for creation of economic policies as response to the crisis, and introduced reforms which helped countries to cope easier with the problems during the crisis. One of the solutions was an increased quote of the member countries and bigger loans as a key step in efforts to overcome the economic crisis. During 2009 and 2010, the member countries provided the Fund with additional 170 billion of Special Drawing Rights (SDRs) through billateral arrangements, which were then included in enlarged New arrangements to borrow.
In order to support the countries during the crisis the IMF has modified its lending frame with the aim to adapt to the countries' needs. The emphasis of this modification was the importance of crisis prevention and rationalisation of the conditions for programms approach. -Stand-by credit facility intended for short-term needs of the balance of payments and for precaution needs -Rapid Credit Facility (RCF) foreseen for urgent balance of payments needs due to external shocks, natural disasters, in events when programmes are either unnecesary or unfeasible.
Source: IMF 2010", adapted by the author In response to the crisis the IMF has implemented policy reforms and has provided for the risk analysis and counselling in the filed of policies in order to help the member countries to overcome the challanges and spill-overs of the global financial crisis. It has also implemented numerous initiatives for strengthening and adjustment of the surveillance over the more globalized and internationally connected world. In order to strenghten its legitimacy, during April 2008 and November 2010 the IMF complied with broad administration reforms as response to the increasing importance of the emergening countries. These reforms enabled even smaller emerging countries to maintain their influence in the IMF (IMF 2016).

CONCLUSION
The modern world economy is characterised by decreasing number of national currencies, which is a logical consequence of increasing international economic and monetary integrations. Respecting the fact that domestic currency is a constituent part of the country's sovereignty capable of actively influencing the real economy, a stable and convrtible national currency is regarded as a reliable measure of economic value and sucess of the economic system, particularly in monetary policy.
The increasing power of the USA economy in the after-war period as well as the status of the US dollar as the world re se rve currency in the Bre tton-Woods system imposed it as a le ading currency. Taking into account the fact that the USA represented the biggest world economic power, the majority of international exchange rate transactions was conducted in US dollars. However, the adoption of the euro as the EMU currency has led to its affirmation in trade affairs in Europe and also in the world. As a stable currency of a huge currency area, the euro has quickly earned favour with business entities of the new eurozone members.
In this research paper we have pointed out to economic, social and political heterogeneity of the union member countries which may pose an obstacle in the establishment of the optimal area of a commmon currency as the highest level of monetary integration. But however, common interests and new world order are creating an idea of the establishment of a monetary union deriving from the fact that monetary integration has significant economic advantages from introduction of a common currency. Decrease in transaction costs, higher price transparency and monetary stability have more benefits in relation to costs of the replacement and introduction of a new currency. But history has shown that monetary unions, beside economic ones, were most often a result of political unions and compromise and the same can be said for the European Monetary Union as well. The monetary integration in Europe was established with the aim to bring about economic prosperity and political stability throughout Europe.
In this research we have analysed the initial stages of the development of a modern international monetary system and its most significant stages and changes. We have pointed out to the fact that m one tary systems, although based on mone tary policy in their nature , are actually a reflection of broader social, economic and international relations. The increasing role of a respective country is measured by the increase in participation of its currency in international transactions, capital flows and international foreign exchange reserves. As this research has shown, turbulances and volatility of the leading world currencies may cause larger market disturbances, influencing either directly or indirectly real economic movements and fiscal parameters of the countries. Therefore it is necessary to secure conditions for a stable international monetary system and an efficient international monetary medium.
Respecting the significance and prescribed criteria for accession to the monetary union we can notice that the countries demonstrated initial differences in real parameters, which creates an unstable basis for further development and success of the functioning of monetary union. Therefore, in the recent literature this has been defined as one of the key reasons for debt crisis. In view of this, in this research paper we have pointed out also to negative effects of the recent global crisis on further process of the monetary integration and stability of the monetary system.