Place: Washington, D.C.
When President James K. Polk requests $2,000,000 on August 8, 1846, to negotiate peace with Mexico, the House of Representatives held a special session. A group of Democrats, led by David Wilmot, proposed an amendment subsequently known as the Wilmot Proviso. Using language largely borrowed from the 1787 Northwest Ordinance, it barred slavery from all territory acquired from Mexico. The bill passed the House with the amendment intact, although votes split almost entirely along sectional lines. The Senate took it up the following day but an attempt to preserve the amendment by delaying the vote until the end of the day backfired and no vote was ever taken. The issue was taken up again in February 1847, when Polk renewed his request (this time asking for $3,000,000). Preston King reintroduced the Wilmot Proviso and it again passed the House. The Senate, however, passed a version of the bill without the Proviso and sent it back to the House. The unamended version passed the House this time, primarily because some northern Democrats changed their votes. The issue surfaced one final time in 1848, when the Senate debated making the Wilmot Proviso part of the Treaty of Guadalupe-Hidalgo but failed.
Michael A. Morrison, Slavery and the American West: The Eclipse of Manifest Destiny and the Coming of the Civil War (Chapel Hill: University of North Carolina Press, 1997), 39-95; William J. Cooper, Jr., The South and the Politics of Slavery, 1828-1856 (Baton Rouge: Louisiana State University, 1978), 227-268; Michael F. Holt, The Political Crisis of the 1850s (New York: John Wiley & Sons, 1978), 56-64.