On December 29, 1845, the United States admitted Texas as the 28th state in the Union. Texas had been an independent republic since 1836 after breaking away from Mexico. Annexation was a major political issue, partly because it involved the expansion of slavery and raised tensions with Mexico. Supporters argued that Texas fit the vision of U.S. territorial growth and would strengthen the nation’s economy and security. Critics worried about war with Mexico and the balance between slave and free states. The annexation contributed to the outbreak of the Mexican-American War in 1846.
