The only one's who had a right to rebel on the basis of the Declaration of Independence were the slaves.
Which of course has nothing at all to do with whether secession is legitimate, America having been born in secession from the British Empire, or whether London held the moral high ground because they proclaimed emancipation for the slaves.
Not to mention that the author of the Declaration was himself an owner of slaves, which is conveniently ignored by those seeking to use the document as addressing slavery.
Oh, but they did!
And unlike our modern pro-Confederates the original secessionists of 1861 had no bashfulness in expressing their true feelings!
At the same time they declared secession several states also wrote up "Declaration of the Immediate Causes Which Induce and Justify the Secession" and these all focus almost exclusively on slavery.
See my post #144 for a link to the Mississippi reasons.