Wilmot Proviso, congressional proposal to prohibit the extension of slavery into newly acquired U.S. territories. In 1846 President James K. Polk asked Congress to appropriate $2 million for Mexico to settle territorial claims. The Wilmot Proviso was the condition some members of Congress tried to impose in return for this payment. The proposal was defeated by the Senate, and the conflict was not resolved until 1862, when Congress outlawed slavery in all U.S. territories.
See also: Slavery.