You couldn't catch a lie if it was glued to your hand, Walt. The issue is secession's constitutionality. Constitutionality supersedes legality.
The Supreme Court ruled in the Prize Cases that secession was not allowed under U.S. law. They ever referred to the "so-called Confederate states".
More from the Court:
"After such an official recognition by the sovereign, a citizen of a foreign State is estopped to deny the existence of a war with all its consequences as regards neutrals. They cannot ask a Court to affect a technical ignorance of the existence of a war, which all the world acknowledges to be the greatest civil war known in the history of the human race, and thus cripple the arm of the Government and paralyze its power by subtle definitions and ingenious sophisms.
The law of nations is also called the law of nature; it is founded on the common consent as well as the common sense of the world. It contains no such anomalous doctrine as that which this Court are now for the first time desired to pronounce, to wit: That insurgents who have risen in rebellion against their sovereign, expelled her Courts, established a revolutionary government, organized armies, and commenced hostilities, are not enemies because they are traitors; and a war levied on the Government by traitors, in order to dismember and destroy it, is not a war because it is an 'insurrection.' "
In fact, it was a war, and it was started by traitors. Those traitors were acting outside the law of the United States. Attempts at unilateral state secession are treason.
Walt