The siege of Béxar was an early campaign of the Texas Revolution in which a volunteer Texian army defeated Mexican forces at San Antonio de Béxar. Texians had become disillusioned with the Mexican government as President and General Antonio López de Santa Anna's tenure became increasingly dictatorial. In early October 1835, Texas settlers gathered in Gonzales to stop Mexican troops from reclaiming a small cannon. The resulting skirmish, known as the Battle of Gonzales, launched the Texas Revolution. Men continued to assemble in Gonzales and soon established the Texian Army. Despite a lack of military training, well-respected local leader General Stephen F. Austin was elected commander.

The Texas Revolution was a rebellion of colonists from the United States and Tejanos against the centralist government of Mexico in the Mexican state of Coahuila y Tejas. Although the uprising was part of a larger one, the Mexican Federalist War, that included other provinces opposed to the regime of President Antonio López de Santa Anna, the Mexican government believed the United States had instigated the Texas insurrection with the goal of annexation. The Mexican Congress passed the Tornel Decree, declaring that any foreigners fighting against Mexican troops "will be deemed pirates and dealt with as such, being citizens of no nation presently at war with the Republic and fighting under no recognized flag". Only the province of Texas succeeded in breaking with Mexico, establishing the Republic of Texas. It was eventually annexed by the United States.