On December 29, 1845, Texas became the twenty-eighth state to join the United States of America when U.S. President James K. Polk signed the Ordinance of Annexation. Texas had a complicated path to statehood, because it had formerly been part of Mexico and then an independent republic. The U.S. Congress passed the Annexation of the Republic of Texas Joint Resolution on March 1, 1845. Voters in Texas then approved the Ordinance of Annexation in October, before it was approved by the U.S. Congress and signed into law by President Polk on this day in 1845.
The U.S. Supreme Court later ruled in Texas v. White that, despite its unique path to statehood, Texas did not have the right to secede from the union.