Wilmot Proviso, a proposed restriction on the extension of slavery in territory obtained by the United States through the Mexican War. To make peace, President Polk asked Congress in 1846 for funds to compensate Mexico for territory that the United States intended to keep. The Wilmot Proviso, presented by Representative David Wilmot, was an amendment to the appropriation bill.

The House twice adopted the amendment, but the Senate did not, and the money was provided without amendment in 1847. Debate over the amendment was heated in Congress and in the nation, and added to the tension between North and South. When the Republican party was formed, it adopted the principle of the Wilmot Proviso with regard to all new territories.