• Minor parties (third parties) exist in the American political system
• But they seldom wield great influence or achieve electoral success
• The most successful third-party movements tend to be co-opted into one of the two major parties

All this, however, does not mean that minor parties are insignificant. In fact, they have on several occasions advanced the national dialogue surrounding specific issues by assuming more creative or extreme positions. The Populist Party of the 1890s was the first to propose a comprehensive package of regulatory measures in response to the social and economic turmoil caused by America's rapid industrialization. But often, the viable proposals of a minor party are quickly absorbed by a major party, helping to achieve the minor party's aims without helping the minor party itself. Both the Republicans and the Democrats stole portions of the Populist agenda, quickly bringing an end to the Populist Party. But during its brief existence, the Populists inspired a shift in the national consensus, forcing the major parties to debate the details and range of government intervention in the economy.

Furthermore, even though two parties have dominated American politics, the two parties have changed periodically. American political history can be broken into a series of eras in which different pairs of major parties have dominated American politics.