The treaty that ended the war between the United States and Mexico in 1848 is the Treaty of Guadalupe Hidalgo. Signed on February 2, 1848, it marked the conclusion of the Mexican-American War, which had begun in 1846. Under the terms of the treaty, Mexico ceded a large portion of its territory to the United States, including present-day California, Arizona, New Mexico, Nevada, Utah, and parts of Colorado and Wyoming. In return, the U.S. agreed to pay $15 million and assumed certain claims against Mexico. This treaty significantly expanded U.S. territory and was a pivotal moment in the westward expansion of the country, shaping its future development.