The treaty that granted the U.S. territory in the Southwest was the Treaty of Guadalupe Hidalgo, signed on February 2, 1848. This treaty concluded the Mexican-American War and led to significant territorial gains for the United States, including present-day California, Nevada, Utah, Arizona, and portions of Colorado and New Mexico. In exchange, the U.S. paid Mexico $15 million and assumed certain claims of American citizens against the Mexican government. This expansive acquisition fueled debates over slavery and ultimately contributed to tensions leading up to the American Civil War.