Unfortunately, this is not a Constitutional way to leave the Union. You conveniently gloss over that fact.
And you seem to try to apply the Constitution for an illegal war that was waged outside of Constitutional limits. You "gloss over" Lincoln's culpability for an illegal war of aggression, and seem to want for the only people that understand the real reason for Southern secession to see it your way. Once again I reiterate, the ideals expressed in the Declaration of Independence are (key words here) fundamental American beliefs ... you know ... 'and are endowed by their Creator with certain inalienable rights, among these are life, liberty, and the pursuit of happiness. ... that governments are created by consent of the governed, and when a government becomes destructive of these ends, it is the RIGHT OF THE PEOPLE TO ALTER OR ABOLISH IT'. Now you will say that these beliefs are not expressed in the Constitution, and I say that they are the bedrock foundation of our American liberty, and comes from a higher authority than the US Constitution just as the Founder's believed they were.