There are profound structural reasons why there are only two electorally viable political parties in the United States. Most elections in the United States use a plurality voting system with single-member districts. Plurality voting means that whoever gets the highest percentage of votes wins, even if it's less than 50%. read more
There are only two mainstream parties because the system of government is designed for only two parties. The two parties have to have carefully formed coalitions of completely different groups of people in order to achieve over 50% of the vote. read more
The answer is that the U.S. political system is set up for two major parties, because it awards seats in Congress and the presidency with a winner-take-all method. Candidates running for Congress need only to get a plurality of the vote to be elected. read more