The Republican Party, also referred to as the GOP ("Grand Old Party"), is one of the two major contemporary political parties in the United States. The GOP was founded in 1854 by anti-slavery activists who opposed the Kansas–Nebraska Act, which allowed for the potential expansion of chattel slavery into the western territories. Since Ronald Reagan’s presidency in the 1980s, conservatism has been the dominant ideology of the GOP. It has been the main political rival of the Democratic Party since the mid-1850s.
The Republican Party’s intellectual predecessor is considered to be Northern members of the Whig Party, with Republican presidents Abraham Lincoln, Rutherford B. Hayes, Chester A. Arthur, and Benjamin Harrison all being Whigs before switching to the party, from which they were elected. The collapse of the Whigs, which had previously been one of the two major parties in the country, strengthened the party’s electoral success. Upon its founding, it supported classical liberalism and economic reform while opposing the expansion of slavery.