Answer:
Two party system
Step-by-step explanation:
The party system in which only two parties are present is called two party system and one of the two parties is called majority party as it have the majority in the legislature, the other one having minority is called oppostion party.
United states is a two party system because all the elected officials belong to one of the two parties. In US Republican and Democratic party are two major parties, Green Libertarian and Constitution are other parties present in US. Most voters choose either Democrats or Republicans, other parties receive minimal support.
Winner takes all is the major factor that helped in making it a two party system. In this system there are grim chances for a third party candidate to win the election. Political scientists have been debating why country with free election evolve into two party system, according to Duverger's law the winner takes all voting system results in a two party system.