further more - it is an argument that the larger lasting impact of that war was about much more then slavery. Every 5-4 decision we see come down from SCOTUS is a remnant of a war that turned a constitution into a bunch of contradictory words that can no longer be agreed on.
Slavery was not going to last much longer regardless, even if the South were allowed to break free. What else was settled was we do not actually believe in the Spirit of 1776 - that was propaganda to get a bunch of people to fight a war for transfer of power
I think the Constitution could not be agreed upon early in our history (McCulloch, Marbury).