Texas and the Mexican-American War

American settlers had been moving into the Mexican territory of Texas since the 1820s, and by 1836 tensions over slavery (which Mexico had outlawed) and self-government boiled into the Texas Revolution. A small force of Texan defenders, including Jim Bowie and Davy Crockett, held the Alamo mission in San Antonio for thirteen days in February-March 1836 before Mexican forces under General Santa Anna overwhelmed and killed them all -- but "Remember the Alamo" became a rallying cry, and Sam Houston's army defeated and captured Santa Anna at the Battle of San Jacinto weeks later, winning Texas its independence.

Texas asked to join the United States right away, but the annexation question was delayed for nearly a decade partly because Texas would enter as a slave state, upsetting the sectional balance in Congress. The U.S. finally annexed Texas in 1845, and a border dispute -- Mexico said the border was the Nueces River, the U.S. claimed the Rio Grande farther south -- helped trigger the Mexican-American War in 1846. American forces under Generals Zachary Taylor and Winfield Scott won battle after battle, ultimately capturing Mexico City itself in 1847. The 1848 Treaty of Guadalupe Hidalgo ended the war: Mexico ceded a huge stretch of land known as the Mexican Cession -- California, Nevada, Utah, most of Arizona and New Mexico, and parts of Colorado and Wyoming -- for $15 million, with the Rio Grande set as the Texas border. Mexican citizens living in the ceded territory were promised U.S. citizenship and protection of their property, promises that were often not honored fairly in the years that followed.