DAVID WILMOT
Until the Civil War, every territorial issue in American politics was colored by the slavery question. The South, even with its advantage of counting slaves as three-fifths of a person was inexorably losing proportional Congressional strength as the growth rate of the free states was much greater. So there would be a pro-slavery movement in every new territory. Wilmot and others were determined that after slavery had been outlawed for two decades in California before the territory became affiliated with the United States, that slavery not be reintroduced which is just what the Southern pro-slavery forces were trying to do. The amendment passed handily in the House but was killed in the Senate where Southern strength was proportionately stronger.
David Wilmot was an American politician and judge. He served as Representative and a Senator for Pennsylvania and as a Judge of the Court of Claims. He is best known for being the prime sponsor and namesake of the eponymous Wilmot Proviso, a failed proposal to ban the expansion of slavery to western lands gained in the Mexican Cession. A notable member of the anti-slavery Free Soil Party, Wilmot later was instrumental in establishing the Republican Party in Pennsylvania.