Major differences between the political system of the United States and that of most other developed democracies are the separation of powers between the legislature and the executive government, and the dominance of the two main parties – the United States being one of the world''s developed democracies in which third parties have the least political influence. ''''No democratic system exists with an absolute separation of powers or an absolute lack of separation of powers. Nonetheless, some systems are clearly founded on the principle of separation of powers, while others are clearly based on a fusion of powers.'''' (wikipedia) Since the Civil War, they have been the Republican and Democratic parties. Minor or third political parties appear from time to time. They advocate policies that eventually are adopted by the two major political partie (Socialist Party, the Farmer Labor Party and the Populist Party for a few years had considerable local strength, then disappeared). So basically the country can function with two major parties because some other interests are presented by third parties which are adopted later on by either one of the two main parties.