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.