The right of a State to be protected from the aggressions of another. The absolute right of a State to self determination. All states were protected by the Constitution from internal aggression by the Federal Government. This was not being done. Abolitionist terrorist were financed, armed, and protected by New England States. This was the belief. Invading a State with another States militia for the purpose of controlling its government and people is unconstitutional. Definition of a State by the Constitution, is "The People" or the sovereign political body of people within a geographical location. States... or "people" have an absolute right to resist other States "people" who attempt to physically control them. It does not matter what a State has legally for its economic engine or what culture it practices, no State or group of States has the right to force another to do anything, even to obey the orders of the Federal Government.
Any sovereign state that determines that it is no longer in its best interest to belong to dysfunctional union has the right to leave it. Self determination.... This is upheld by International Law and the Law of Nations. It comes from the Declaration of Independence.