Texas was annexed by the United States on December 29, 1845 and was admitted to the Union as the 28th state on that day, with the transfer of power from the Republic to the new state of Texas formally taking place on February 19, 1846.
"In 1844, Congress finally agreed to annex the territory of Texas. On December 29, 1845, Texas entered the United States as a slave state, broadening the irrepressible differences in the United States over the issue of slavery and setting off the Mexican-American War."
