The treaty that ended the Mexican-American War was the Treaty of Guadalupe Hidalgo, signed on February 2, 1848.

This agreement marked a significant turning point in U.S. history, as it resulted in Mexico ceding a vast portion of its territory to the United States, including present-day California, Arizona, New Mexico, Nevada, and Utah. In exchange, the U.S. agreed to pay $15 million and assume certain claims of American citizens against Mexico. The treaty not only expanded U.S. territory but also intensified debates over slavery and contributed to the sectional tensions that led to the Civil War.