The Treaty of Guadalupe Hidalgo officially ended the Mexican–American War (1846–1848). It was signed on 2 February 1848 in the town of Guadalupe Hidalgo.
After the defeat of its army and the fall of the capital in September 1847, Mexico entered into peace negotiations with the U.S. envoy, Nicholas Trist. The resulting treaty required Mexico to cede 55 percent of its territory including the present-day states of California, Nevada, Utah, and most of Colorado, New Mexico, and Arizona. Mexico also relinquished all claims for Texas and recognized the Rio Grande as the southern boundary of Texas.
In turn, the U.S. government paid Mexico $15 million "in consideration of the extension acquired by the boundaries of the United States" and agreed to pay American citizens debts owed by the Mexican government. Mexicans in areas annexed by the U.S. could relocate within Mexico's new boundaries or receive American citizenship and full civil rights.
The United States ratified the treaty on 10 March and Mexico on 19 May. The ratifications were exchanged on 30 May, and the treaty was proclaimed on 4 July 1848.
The U.S. Senate ratified the treaty by a vote of 38–14. The opponents of this treaty were led by the Whigs, who had opposed the war and rejected manifest destiny in general, and rejected this expansion in particular. The amount of land gained by the United States from Mexico was further increased due to the Gadsden Purchase of 1853, which ceded parts of present-day southern Arizona and New Mexico to the United States.
Nicholas Trist negotiated the peace talks; Trist, the chief clerk of the U.S. State Department, accompanied General Winfield Scott as a diplomat and President James K. Polk's representative. After two previous unsuccessful attempts to negotiate a treaty with General José Joaquín de Herrera, Trist and General Scott determined that the only way to deal with Mexico was as a conquered enemy. Trist negotiated with a special commission representing the collapsed government led by Don José Bernardo Couto, Don Miguel de Atristain, and Don Luis Gonzaga Cuevas of Mexico.