An effort to keep slavery from spreading.
From 1846-48, the U.S. was at war with Mexico. This was a war that Democratic President James K. Polk forced on Mexico so the U.S. could defeat them and take land from them. The U.S. would end up taking more than half of Mexico’s existing land.
David Wilmot was a Pennsylvania Congressman from the Whig Party, which opposed the war. They saw it as an effort by Polk to get land so that slavery could eventually spread into the land. Wilmot suggested a law that would not allow slavery to exist in any land gained from Mexico in the war.
The bill passed the House but was defeated in the Senate. It was another example of how the North and South differed on nearly everything involving slavery.
Among politicians who opposed the war were Whig Congressmen John Quincy Adams and Abraham Lincoln.