United States: Political Parties & Elections

Since the mid-nineteenth century, American national politics has been dominated by two parties, the Democratic Party, founded in 1828, and the Republican Party, founded in 1854. Together they have won every U.S. presidential election since 1852 and have controlled Congress in nearly every session since the 1850s, making the United States one of the world's most enduring examples of a stable two-party system.

Political scientists commonly divide the country's party history into a series of party systems, each marked by shifting coalitions and issues even as the two major parties' names endured: an early First Party System pitting Federalists against Democratic-Republicans, a Second Party System of Democrats against Whigs, and successive realignments through the Civil War, the Progressive Era, the New Deal, and the modern era beginning in the late 1960s. Over these transformations, both major parties changed considerably in their regional bases and ideological commitments.

Structural features of American elections help sustain this two-party dominance. Most offices, including seats in Congress, are elected from single-member districts by a simple plurality, an arrangement that political scientists have long observed tends to favor two dominant parties over multiple smaller ones. Additional factors, such as state ballot-access laws requiring substantial petition signatures, further raise the bar for third parties such as the Libertarian, Green, and Constitution parties, which compete regularly but have rarely achieved major electoral success.