Czech Republic–Slovakia relations
Before 1918, both countries were part of Austria–Hungary. However, after the Ausgleich of 1867 Czechia belonged to the Austrian Empire while Slovakia belonged to the administratively separate Kingdom of Hungary, and between 1918 and December 31, 1992, both countries were part of Czechoslovakia. 
Both countries established diplomatic relations on January 1, 1993. These international relations are usually referred to or described as "very good", "cordial", and "above standard" in the media. When a Czech or Slovak president is inaugurated, very often his first international visit is to the former part of the common country. The same custom applies to newly elected prime ministers of the Czech Republic and Slovakia.
History of Czechoslovak nationality
After World War I, the First Czechoslovak Republic was finally formed by combining the Czech lands, Upper Hungary, and Carpathian Ruthenia, which was annexed in 1919 due to the Allies’ pressure. If the desire for a Czechoslovak nation had been expressed for a long time, the Slovaks in the 1920s, nevertheless, felt resentment because they were proportionally less represented into the Czechoslovak administration. This, however, can be explained by the fact that, in Austria-Hungary, the Czechs had the opportunity to develop an elite which could then lead the new country and that such an elite was totally absent in the Slovak population. Moreover, the formation of a Czechoslovak Hussite Church which conducted its services in Czech created large discontent. New national holidays, such as July 6, which commemorated the death of Czech reformer Jan Hus, created opposition within the Catholics. Also during the 1920s, the Slovaks became more and more literate, thus developing their own culture, and the structures promoting such a Slovak culture.