The Mexican-American War reopened the slavery-extension issue, which divided the North and South and which had been largely dormant since the Missouri Compromise. Abolitionists saw the war as an attempt by the slave states to extend slavery and enhance their power with the creation of additional slave states out of the soon-to-be-acquired Mexican lands. On August 8, 1846, Rep. David Wilmot of Pennsylvania attempted to add an amendment to a treaty appropriations bill. The Wilmot Proviso—banning slavery from any territory acquired from Mexico—was never passed, but it led to acrimonious debate and contributed greatly to the rising sectional antagonism.
Mexican-American War Article