Wilmot Proviso (Amendment to HR 534, 29th Congress), August 8, 1846
Representative David Wilmot proposed the controversial amendment to the appropriations bill ending the Mexican War. Known as the Wilmot Proviso, his amendment would have prohibited slavery in any territory acquired from Mexico. Passed by the House, but not by the Senate—where southern opposition was stronger—the proviso intensified the sectionalism that precipitated the Civil War.
Records of the U.S. House of Representatives, National Archives and Records Administration
Provided that, as an express and fundamental condition to the acquisition of any territory from the Republic of Mexico, by the United States,… neither slavery nor involuntary servitude shall ever exist in any part of said territory
Slavery in the West
Westward expansion stoked tensions in Congress as Northern and Southern factions disputed whether to allow slavery in new territories. In 1846, during the Mexican War, Representative David Wilmot of Pennsylvania attempted to limit slavery in the West through an amendment to a war appropriations bill. His proviso, banning slavery in any territories acquired from Mexico, passed the House but not the Senate. The Wilmot Proviso––included in subsequent House bills but never enacted—kept slavery at the forefront of congressional debate.