Texas was...

... part of Mexico, was it's own republic, became a US state, was part of the Confederacy and then was back in the USA

March 30th, 1870 -- Congressional Reconstruction ends as Texas readmitted to Union

On this day in 1870, U.S. President Ulysses S. Grant signed the act that ended Congressional Reconstruction and readmitted Texas to the Union. In the aftermath of the Civil War, Texas had been in turmoil, first under Presidential Reconstruction and then, beginning in 1867 with the passage of the First Reconstruction Act, under Congressional Reconstruction. The latter required that Texas have a constitutional convention, with delegates elected by all male citizens over the age of twenty-one, regardless of race, color, or "previous condition of servitude." The convention was to write a new state constitution that would provide for universal adult male suffrage. When the constitution had been written and the state had ratified the Fourteenth Amendment of the United States Constitution, Congress would consider the case for readmission to the Union. The convention met at Austin in June 1868 and did not adjourn until February 1869. The constitution it produced differed significantly from previous constitutions by authorizing a more centralized and bureaucratized system of government, with greater power in the hands of the governor. In February 1870 the Twelfth Legislature assembled at Austin to adopt the Fourteenth and Fifteenth amendments and select United States senators in preparation for readmission to the Union. They quickly approved the amendments and selected Morgan C. Hamilton for a six-year term and James W. Flanagan for a four-year term. This completed the requirements set by Congress for readmission.
Source: Texas Day by Day