Before Texas became a member of the United States, it was its own country: The Republic of Texas. (And before that, it had been claimed by Spain, France, and Mexico.) But in 1845, things began to change, and on July 4th of that year, the Texas Congress passed an ordinance agreeing to an annexation offer from the Union. The citizens of Texas approved the annexation ordinance on October 13, 1845, and on December 29, 1845, President James Polk made the former republic an official state. On February 14, 1846, Texas formally relinquished its sovereignty to the U.S.