Two-party system
A two-party system is a party system where two major political parties dominate the government. One of the two parties typically holds a majority in the legislature and is usually referred to as the "majority" or "governing party" while the other is the "minority" or "opposition party". Around the world, the term has different senses. For example, in the United States, Jamaica, and Malta, the sense of "two-party system" describes an arrangement in which all or nearly all elected officials belong to one of the only two major parties, and third parties rarely win any seats in the legislature. In such arrangements, two-party systems are thought to result from various factors like winner-takes-all election rules. In such systems, while chances for third-party candidates winning election to major national office are remote, it is possible for groups within the larger parties, or in opposition to one or both of them, to exert influence on the two major parties. In contrast, in the United Kingdom and Australia and in other parliamentary systems and elsewhere, the term "two-party system" is sometimes used to indicate an arrangement in which two major parties dominate elections but in which there are viable third parties which do win seats in the legislature, and in which the two major parties exert proportionately greater influence than their percentage of votes would suggest.
Greens/Green Party USA
The source of the rift between the two national Green parties is a matter of contentious debate. Some point to differences of political philosophy or views on the proper structure of the party or attitudes toward elections, while others suggest it was more about personality conflicts, turf struggles, and poor communication leading to concerns about financial and political accountability, or perhaps the 1991 name grab or the inaccurate G/GPUSA FEC filing in 1995. It is important to note that the heated debates and the fighting that was waged for several years at the national level (and among Greens within a few states, such as New York, Missouri, California and New Jersey) seemed largely irrelevant to the vast majority of grassroots Greens, who preferred to devote their energies to local organizing.