The tenth Amendment proves perfectly how there was no right to unilateral secession by a state or states.
It specifically says that states (or the People) have powers NOT already delegated to the United States through the Constitution.
The Confederate democrats had no right in anyway to usurp these powers as the tenth Amendment states. The tenth Amendment makes it clear that the states have powers NOT delegated to the United State by the Constitution.
Of course the traitorous Confederate democrats wanted to ignore this Amendment though annd to claim that ALL rights were state rights and that they could could just unilaterally disregard the tenth Amendment and the entire Constitution based upon their immoral and perverted political views.