Two party system

A two-party system is a party system where two major political parties dominate the government. 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 senses. For example, in the United States, Jamaica, and Malta, the sense of two party system describes an arrangement in which all or nearly all elected officials belong to one of the only two major parties, and third parties rarely win any seats in the legislature. In such arrangements, two-party systems are thought to result from various factors like winner takes all election rules. In such systems, while chances for third party candidates winning election to major national office are remote, it is possible for groups within the larger parties, or in opposition to one or both of them, to exert influence on the two major parties. In contrast, in the United Kingdom and Australia and in other parliamentary systems and elsewhere, the term two-party system is sometimes used to indicate an arrangement in which two major parties dominate elections but in which there are viable third parties which do win seats in the legislature, and in which the two major parties exert proportionately greater influence than their percentage of votes would suggest.

The reasons why a country with free elections will evolve into a two-party system have been debated. A leading theory, referred to as Duverger's law, states that two parties are a natural result of a winner-take-all voting system.

There is general agreement that the United States has a two-party system; historically, there have been few instances in which third party candidates won an election. In the First Party System, only the Federalist Party and Thomas Jefferson's Democratic-Republican Party were significant political parties. Toward the end of the First Party System, the Republicans dominated a one-party system (primarily under the Presidency of James Monroe). Under the Second Party System, the Democratic-Republican Party split during the election of 1824 into Adams' Men and Jackson's Men. In 1828, the modern Democratic Party formed in support of Andrew Jackson. The National Republicans were formed in support of John Quincy Adams. After the National Republicans collapsed, the Whig Party and the Free Soil Party quickly formed and collapsed. In 1854, the modern Republican Party formed from a loose coalition of former Whigs, Free Soilers and other anti-slavery activists. Abraham Lincoln became the first Republican president in 1860.

...
Wikipedia