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The Treaty of Guadalupe Hidalgo concludes, but escalates the debate between the North and the South over slavery in the U.S.

1848 (Feb 1)

The Treaty of Guadalupe Hidalgo was concluded between the United States and Mexico, ending two years of combat between the countries. Under the terms of the treaty, the present states of New Mexico and California were ceded to the United States. Many pro-slavery Southerners had supported the war, anticipating that new lands would be opened to slavery. Many anti-slavery Northerners had opposed the war, fearing that it was the result of a pro-slavery conspiracy designed to open new territory to slavery. Shortly after the war began in 1846, democratic representative David Wilmot of Pennsylvania introduced an amendment to a pending bill in Congress—to become known as the "Wilmot Proviso"—which sought to prohibit slavery in any territory acquired as a result of the Mexican war. The proviso passed in the House of Representatives but was defeated in the Senate. The Mexican cession and the status of slavery there precipitated bitter debate between North and South from 1848 to 1850. One proposed solution was offered by President Zachary Taylor, who suggested that California and New Mexico bypass the territorial stage of government and apply directly for statehood, thus nullifying the question of slavery in the Mexican Cession territories. This proposal was unacceptable to the South, for both New Mexico and California would enter the Union as free states, thus upsetting the precarious sectional balance in the U.S. Senate that now stood at fifteen states each. The grounds were laid for the famous Compromise of 1850.