The Constitution does not directly mention secession.
[55] The legality of secession was hotly debated in the 19th century, with Southerners often claiming and Northerners generally denying that states have a legal right to unilaterally secede.
[56] The Supreme Court has consistently interpreted the Constitution to be an "indestructible" union.
[55] There is no legal basis a state can point to for unilaterally seceding.
[57] Many scholars hold that the Confederate secession was blatantly illegal. The Articles of Confederation explicitly state the Union is "perpetual"; the U.S. Constitution declares itself an even "more perfect union" than the Articles of Confederation.
[58] Other scholars, while not necessarily disagreeing that the secession was illegal, point out that sovereignty is often
de facto an "extralegal" question. Had the Confederacy won, any illegality of its actions under U.S. law would have been rendered irrelevant, just as the undisputed illegality of American rebellion under the British law of 1775 was rendered irrelevant. Thus, these scholars argue, the illegality of unilateral secession was not firmly
de facto established until the Union won the Civil War; in this view, the legal question was resolved at
Appomattox.