That is a common falsehood adopted by the Defenders of the Slaverocracy but it has no bearing in fact. The Founders created a perpetual Union only changeable through a Constitutional amendment. States were not allowed to unilaterally change the Union. Madison wrote Hamilton that "once in the Union always in the Union." ALL the Founders believed dissolution to be the greatest evil which could be visited upon the United States.
After the War the USSC ruled secession to be illegal w/o an amendment even Texas which was a special case due to it having truly been sovereign.
It is also a fact that the states were CREATED by the Nation when the independent colonies were instructed by the Continental Congress to write constitutions forming themselves into states. Of course, ALL Southern states other than Va., NC, SC, Ga., were ENTIRELY created by the Congress and have NO pretensions to EVER being sovereign.
I take it you are unfamiliar with the Republic of West Florida, and the origin of the Bonnie Blue flag.