Opposition Party (Northern U.S.)

The Opposition Party was a party identification under which Northern anti-slavery politicians, formerly members of the Democratic and the Whig Parties, briefly ran in the 1850s in response to the expansion of slavery into the new territories. It was one of the movements that arose from the political chaos in the decade before the American Civil War in the wake of the Compromise of 1850. The movement had arisen before and was quickly subsumed by the coalescence of the Republican Party in 1856.

During the fragmenting of the Second Party System of Jackson Democrats and Clay Whigs, the Democratic efforts to expand slavery into western territories, particularly Kansas, led to organized political opposition, which coalesced in Congress as the "Opposition Party." As the Whig Party disintegrated, many local and regional parties grew up, some ideological and some geographic. When they realized their numbers in Congress, they began to caucus in the same way that US political parties had arisen before the Jacksonian national party conventions. Scholars such as Kenneth C. Martis have adopted a convention to explain the congressional coordination of anti-Pierce and anti-Buchanan factions as the "Opposition Party."