Duopoly

Duopoly is a form of oligopoly where only two producers are present in a given market.

Modern US politics has been described as a duopoly since the Republican and Democratic Parties have dominated and framed policy debate. They have shaped, by default, matters of national concern for about a century and a half.

See List of political parties in the United States for a more comprehensive look at the politics of the Two-party system, Duverger's law.