In post 1055 you stated, The acts of secession were legislation passed by the Texas legislature, and which violated the Constitution. The Texas Legislature might have approved the secession act, but that does not mean it was an act of the legislature.
Approval of actions concerning the status of states was a power delegated to the United States Congress by Article IV of the Constitution.
Can you post the clause prohibiting a state from divesting itself of lands to a foreign country? Can you post the clause prohibiting a state from seceding? Can you post the clause prohibiting a state from enlarging it's borders?
I did, specifically clause 2.
Again, the people of each state are not bound by the Supremacy clause. Even then, what power has been delegated to the federal government to coerce a state official? If the public official, including the governor of the state,
'refuses to discharge this duty, there is no power delegated to the General Government, either through the Judicial Department or any other department, to use any coercive means to compel him.'
Chief Justice Taney, Kentucky v. Dennison, 65 US 66 (1860)
The first one is easy. Article I, Section 10, Clause 3: "No State shall, without the Consent of Congress,...enter into any Agreement or Compact with another State, or with a foreign Power..." The third one is easy as well, and is covered by the same clause since adjusting borders requires agreements between the states. The second one is just as easy. While there is nothing in the Constitution that prohibits secession, unilateral actions like leaving the Union would be prohibited since Congressional approval is necessary for changing the status of a state.
Again, the people of each state are not bound by the Supremacy clause.
They are, but more specifically their legislatures are. And legislation passed by Texas in support of secession, and in support of the rebellion, was unconstitutional.