the incorporation of the Republic of Texas into the United States of America. In 1836 the Texian Army won the Battle of San Jacinto against Mexican forces, led by famed general Santa Anna, and the Republic of Texas declared its independence from Mexico. But Mexico had refused to acknowledge this action and warned the U.S. that if it tried to make Texas part of the U.S., Mexico would declare war. In 1845 Texas voluntarily asked to join the U.S., and became the 28th state. This action led to Mexico to declare war on the United States, starting the Mexican-American War.