I can see where Article 4 Section 3 could apply.
New states may be admitted by the Congress into this union; but no new states shall be formed or erected within the jurisdiction of any other state; nor any state be formed by the junction of two or more states, or parts of states, without the consent of the legislatures of the states concerned as well as of the Congress.
The Congress shall have power to dispose of and make all needful rules and regulations respecting the territory or other property belonging to the United States; and nothing in this Constitution shall be so construed as to prejudice any claims of the United States, or of any particular state.
But that presupposes that the state in question is a member of the union. If that state has seceded then it will no longer apply.
I see nothing in Articles 1 or 4 that restricts unilateral secession. I can only understand State Sovereignty in the context of voluntary membership in the union. Anything less is not statehood.
That is not an argument
But is an accurate description.
I assumed we were having a friendly debate. I believe I am making factual arguments. If I am wrong I will admit it if you show me factual rebuttal.
As I said, Article I and Article IV give Congress the power to admit new states and approve any change in their status - by splitting, combining, or any change in their territory - once they have been admitted. Implied in that is the power to approve any change at all, including leaving.
I can only understand State Sovereignty in the context of voluntary membership in the union.
You say it's voluntary, yet a state is admitted only with the permission of the other states. No other party really has a say in the matter; not the president or the courts or even the people of the territory itself. So membership is not voluntary, it is granted. Since a new state has to have permission to join why is it so hard to accept it needs permission to leave as well?
If I am wrong I will admit it if you show me factual rebuttal.
Saying the attack on Fort Sumter was a defensive measure is complete nonsense. The fort posed no threat to the people of Charleston. It had taken no aggressive actions. It had not interfered with a single ship entering or leaving. It had done nothing to prompt a defensive measure. On the contrary, the South tried to starve it into surrender. The South fired on ships entering the harbor on more than one occasion. The South was making unreasonable demands. It was the South who was the aggressor and not the North.