The Treaty of Guadalupe Hidalgo, signed in 1848, concluded the Mexican-American War and had profound implications for both nations. It resulted in Mexico ceding a significant portion of its territory to the United States, including present-day California, Nevada, Utah, Arizona, and parts of Colorado and Wyoming. In exchange, the U.S. agreed to pay $15 million and assume certain claims of American citizens against Mexico. The treaty significantly expanded U.S. territory, fueling debates over slavery's expansion into new states and intensifying sectional tensions, which ultimately contributed to the onset of the American Civil War.