Even with the loss of the Alamo, Texas declared its independence from Mexico on March 2, 1836. On April 21, Sam Houston's troops attacked, while Santa Anna was having his siesta. The battle cry, "Remember the Alamo; Remember Goliad" has lived on. The Republic of Texas was recognized by the United States, Britain, France, Holland, and Belgium. The fledgling state soon struggled under financial problems, raids by Mexican forces, and wars with natives.

In September 1836, Texas voted for annexation by the United States. U.S. congressional approval was delayed for nine years because of opposition to the extension of slavery by the Northern states. On December 29, 1845, Congress accepted the Texas state constitution and Texas was admitted to the Union. The Mexican War, between the United States and Mexico, followed Texas statehood by only a few months. U.S. success in that war established the Rio Grande River as the border between the two countries, although Texas claimed all territory between the mouth of the river to its source in southern Colorado. As part of the Compromise of 1850, Texas relinquished its claim to about half of what today is New Mexico and portions of Colorado, Kansas, Oklahoma, and Wyoming for $10 million.

Texas seceded from the Union on February 1, 1861, and was re-admitted on March 30, 1870, after ratifying the 13th, 14th, and 15th Amendments to the U.S. Constitution.