In 1803, by the Louisiana Purchase, the United States acquired land west of the Mississippi. To the southwest it adjoined Texas, which American adventurers were inclined to treat as unclaimed territory. There were several clashes between Spanish authorities and intruders. However, in 1821 the Spanish granted permission to Moses Austin to settle a group of American families in Texas.

The American colony was established late in 1821 by Austin's son, Stephen F. Austin, who had his father's grant confirmed by newly independent Mexico. The original quota of 300 families was settled in the region west of present Houston. Austin obtained additional grants, and other American colonizers were permitted to bring in groups of no less than 200 families each. Soon the Americans far outnumbered the Mexicans. In 1832 the settlers petitioned Mexico to divide the state of Coahuila-Texas into two separate states and to give Texas privileges such as use of English in official business and its own militia.

When Mexico proved hostile to the settlers' desires and even jailed Austin briefly as a revolutionary, the Texans decided to fight for self-government. They attacked and defeated a Mexican force, sent to maintain authority, at Gonzales in October, 1835, and the next month formed a provisional government. San Antonio, the Mexican administrative center, was captured by the Texans in December. On March 2, 1836, Texas was declared an independent republic.

Meanwhile, the Mexican general Santa Anna had marched northward to put down the revolt. He arrived at San Antonio on February 23, 1836, and laid siege to the Alamo, the town fortress, which was defended by fewer than 200 Texans. After a heroic resistance to the last man, it fell on March 6. Two weeks later a force of Texans was compelled to surrender near Goliad; upon orders of Santa Anna the prisoners were slain.

General Sam Houston, leading the Texas Army, on April 21 attacked the Mexican forces at the San Jacinto River east of present Houston. With “Remember the Alamo! Remember Goliad!” as their rallying cry, the Texans won a quick victory. The capture of Santa Anna ended the conflict.