The event that marked the establishment of the Republic of Texas in 1836 was the Texas Revolution, specifically the victory at the Battle of San Jacinto on April 21. This decisive battle against Mexican forces led to the capture of General Santa Anna and solidified Texas's independence from Mexico. Following the revolution, Texas declared itself a republic, which was recognized by the United States and other nations. The establishment of the Republic set the stage for Texas to later join the Union in 1845, significantly shaping American territorial expansion and introducing complex issues surrounding slavery and statehood.