(1848–54), minor but influential political party in the pre-Civil War period of American history that opposed the extension of slavery into the western territories. Fearful of expanding slave power within the national government, Representative David Wilmot of Pennsylvania in 1846 introduced into Congress his famous Wilmot Proviso, calling for the prohibition of slavery in the vast southwestern lands that had been newly acquired from Mexico. The Wilmot concept, which failed in Congress, was a direct ideological antecedent to the Free-Soil Party. Disappointed by the ambivalent position of the Whig Party toward slavery, “Conscience” Whigs held a convention in August 1848 at Buffalo, N.Y. There they were joined by delegates from 17 states drawn from the Liberty Party (q.v.) and the antislavery faction of the New York Democrats, known as “Barnburners.”. The Free-Soilers' historic slogan calling for “free soil, free speech, free labor, and free men” attracted small farmers, debtors, village merchants, and household and mill workers, who resented the prospect of black-labour competition—whether slave or free—in the territories.