Wilmot Proviso, 1846, amendment to a bill put before the U.S. House of Representatives during the Mexican War; it provided an appropriation of $2 million to enable President Polk to negotiate a territorial settlement with Mexico. David Wilmot introduced an amendment to the bill stipulating that none of the territory acquired in the Mexican War should be open to slavery. The amended bill was passed in the House, but the Senate adjourned without voting on it. In the next session of Congress (1847), a new bill providing for a $3-million appropriation was introduced, and Wilmot again proposed an antislavery amendment to it. The amended bill passed the House, but the Senate drew up its own bill, which excluded the proviso. The Wilmot Proviso created great bitterness between North and South and helped crystallize the conflict over the extension of slavery. In the election of 1848 the terms of the Wilmot Proviso, a definite challenge to proslavery groups, were ignored by the Whig and Democratic parties but were adopted by the Free-Soil party. Later the Republican party also favored excluding slavery from new territories.
See C. W. Morrison, Democratic Politics and Sectionalism (1967).