The war of words for 'causation' whether the war was fought over 'freedom' for the South versus 'dominance' for the North has gone on since before the Civil War itself.

I was taught in no uncertain words in junior high school in the outskirts of Boston that the issue was 'slavery'.

Some, maybe most, of the Americans of Southern origin (and they happened to be of Caucasian extraction) have attempted to make the point with me that the Constitution did not deny them the power to secede, that the States had rights and it was in defense of these rights that they resisted the unconscionable and agressive encroachments of the North.

I happen to feel that, as Lincoln hoped, 'right would make might' and that the Civil War itself and de facto settled the issue in favor of Union.

Lincoln stated the case, as was his wont, with the best logic and the fewest words:

"Those who deny freedom to others, deserve it not for themselves; and, under a just God, can not long retain it."
The Collected Works of Abraham Lincoln edited by Roy P. Basler, Volume III, "Letter To Henry L. Pierce and Others" (April 6, 1859), p. 376.