Final answer:
Texas went through constitutional changes in the 1860s, failing to ratify its state constitution to rejoin the Union until it dealt separately with proscriptive clauses and ratified a new state constitution without them by 1870.
Step-by-step explanation:
During the 1860s, Texas went through various constitutional changes as part of the broader national upheaval during and after the Civil War. Texas, which had been part of the Confederacy, had to revise its state constitutions before it could be readmitted to the Union. After the Civil War, Texas, along with Virginia and Mississippi, initially failed to ratify their state constitutions acceptable to the U.S. Congress.
It was only after the so-called proscriptive clauses, which barred former Confederates from participating in government, were dealt with separately that Grant recommended to Congress that the states should be readmitted.
Consequently, Texas ratified a new state constitution that did not include these proscriptive clauses and also approved the Fifteenth Amendment. This ratification process was completed, and its representatives were seated in Congress by 1870.