“The south was engaged in self-determinism when they turned their backs on their Constitution and countrymen.”
It was common practice for states to reserve to themselves the right to withdraw from the Constitution. They only ratified the Constitution on that condition.
“What they attempted was to force a unilateral (southern) determinism upon the entire continent.”
Nonsense. If Lincoln had not decided to make war, there would have been no war.
There's only one way out of the union - the same way they got in. And that is by mutual accord. Unilateral secession has never been legal.