Events following the Mexican–American War fueled rising tensions between the free and slave states, as proslavery fire-eaters threatened secession in response to the Wilmot Proviso. Their domination of the Democratic Party in the Lower South after 1849 necessitated a political alliance between unionist Democrats and Whigs who sought to avert a civil war and defeat their intrapartisan rivals. Unionists were especially active in the 1851 elections, when Union parties elected 14 members to the House of Representatives and won governorships in Georgia and Mississippi.[3] The acquiescence of the Southern Rights leaders to the Compromise after 1851 removed the need for a dedicated Union party. Many Whigs who had supported the Union Party movement subsequently joined the Democratic Party; most Unionist Democrats returned to their former political allegiance.[4]
In states where Union parties were organized, Unionists supported preservation of the federal Union and opposed an independent Southern Confederacy. Ardently proslavery, they rejected secession as unconstitutional and ruinous to the interests of the slave states.[5] Instead, they advocated a policy of conditional unionism wherein the slave states would remain loyal to the national government so long as the free states agreed to abide by the Compromise and abstain from any future attacks on slavery. While they opposed immediate secession, Unionists did not rule it out in the future should southern demands go unheeded.[6] Many who had been Unionists in the 1850s would go on to serve in the Confederate government during the Civil War, including Alexander H. Stephens, who served as vice president of the Confederacy from 1861 to 1865.[7]
