[DoodleDawg]

I believe it is only the State of Texas that must approve the four additional states. Beyond that, any new state admitted to the union must adhere to the same requirements.

Texas may have been able to do that once the republic signed the treaty with the U.S. and before Texas became a state but that ship has long since sailed. Texas has no more powers under the Constitution than any other state has.

[BuckeyeTexan]

Texas may have been able to do that once the republic signed the treaty with the U.S. and before Texas became a state but that ship has long since sailed.

Texas did not join the Union by treaty. Texas was annexed by a joint resolution of Congress. Texas still has the right to form new states. The JR and Order of Annexation says:

New States of convenient size not exceeding four in number, in addition to said State of Texas and having sufficient population, may, hereafter by the consent of said State, be formed out of the territory thereof, which shall be entitled to admission under the provisions of the Federal Constitution.

Texas has no more powers under the Constitution than any other state has.

The key phrase being under the Constitution. I haven't said otherwise.