The Treaty of Guadalupe Hidalgo (Tratado de Guadalupe Hidalgo in Spanish) is the peace treaty, largely dictated by the United States to the interim government of a militarily occupied Mexico City, that ended the Mexican-American War (1846 – 48) on February 2, 1848. With the defeat of its army and the fall of the capital, Mexico surrendered to the United States and entered into negotiations to end the war.
The peace talks were negotiated by Nicholas Trist, chief clerk of the State Department, who had accompanied General Winfield Scott as a diplomat and President Polk's representative. Trist and General Scott, after two previous unsuccessful attempts to negotiate a treaty with General José Joaquín de Herrera, determined that the only way to deal with Mexico was as a conquered enemy. Nicholas Trist negotiated with a special commission representing the collapsed government led by Don Bernardo Couto, Don Miguel Atristain, and Don Luis Gonzaga Cuevas of Mexico.
Under the terms of the treaty negotiated by Trist, Mexico ceded to the United States Upper California and New Mexico. This was known as the Mexican Cession and included all of present-day California, Nevada and Utah as well as most of Arizona, New Mexico and Colorado. Mexico relinquished all claims to Texas and recognized the Rio Grande as the southern boundary of the United States.
The treaty provided for the Mexican Cession of 1.36 million km² (525,000 square miles) to the United States in exchange for 15 million dollars (equivalent to $380 million today). The Treaty also ceded an additional 1,007,935 km2 (389,166 sq mi), since Mexico had never officially recognized either the independence of the Republic of Texas (1836) or its annexation by the United States (1845), and under this calculation, Mexico lost about 55% of its prewar territory.
The Treaty also ensured safety of existing property rights of Mexican citizens living in the transferred territories. Despite assurances to the contrary, the property rights of Mexican citizens were often not honored by the U.S. in accordance with modifications to and interpretations of the Treaty. The U.S. also agreed to take over 3.25 million dollars (equivalent to $82.2 million today) in debts that Mexico owed to United States citizens.