The Republican Party, also known as the GOP, is one of the two major contemporary political parties in the United States. It emerged as the main political rival of the Democratic Party in the mid-1850s.

A two-party system is a political party system in which two major political parties consistently dominate the political landscape. At any point in time, one of the two parties typically holds a majority in the legislature and is usually referred to as the majority or governing party while the other is the minority or opposition party. Around the world, the term has different meanings. For example, in the United States, the Bahamas, Jamaica, and Zimbabwe, the sense of two-party system describes an arrangement in which all or nearly all elected officials belong to either of the two major parties, and third parties rarely win any seats in the legislature. In such arrangements, two-party systems are thought to result from several factors, like "winner takes all" or "first past the post" election systems. The electoral competition is mostly limited to the two major parties.