The treaty that ended the Mexican-American War in 1848 was the Treaty of Guadalupe Hidalgo. Signed on February 2, 1848, the treaty formalized the cessation of hostilities between Mexico and the United States. As a result of the treaty, Mexico ceded significant territories, including present-day California, Arizona, New Mexico, Nevada, Utah, and parts of Colorado and Wyoming, to the United States. The treaty allowed for the expansion of U.S. territory and fueled debates over slavery in the newly acquired lands, ultimately contributing to tensions leading up to the American Civil War.