Having been an independent nation since 1836, Texas ratified its new constitution in 1845 to become a state within the United States.
It ratified a new constitution in 1861 to become a state in the Confederacy, then a new constitution in 1865 to become a state within the United States again. Texans ratified a new constitution in 1876 as a backlash against what was seen by an abuse of power by a governor. We still have the Constitution of 1876, but it has been amended hundreds of times.