Treaty of Guadalupe Hidalgo (1848)

Saturday, January 01, 1848

Signed by President James K. Polk, this treaty not only ended the Mexican-American War, but the United States annexed 55% of Mexico’s territory (including California, Nevada, Utah, Colorado, and present-day New Mexico and Arizona). This treaty also set the Rio Grande river as the border between Texas and Mexico. As a result, residents of the territory were allowed to choose whether they wanted Mexican or U.S. citizenship by leaving or remaining in the newly formed U.S. territory.