That is the snag in your argument. There was never a circumstance before the war where the south was in jeopardy of destruction. In fact, for most of the period after the unions inception the south played a prominent role in governing our nation.
The slavocracy incited their southern neighbors to insurrection and rebellion - and paid a dear price.
And the Representatives of King George III also thought we were making much ado about nothing. Why didn't the King give the colonists some concessions?
I think it has something to do with what people believed. Sure, the Union government didn't really do anything to endanger Southern Slavery, but I think they could see where things were going. They were outnumbered by representatives of states that had abolished slavery, and they thought destruction of their economic system was only a matter of time.
People act on what they believe, whether it be true or not.
The slavocracy incited their southern neighbors to insurrection and rebellion - and paid a dear price.
What did their "southern neighbors" do that constituted insurrection? Seems to me that it was only South Carolina that fired on Ft. Sumter. The other states did nothing until the Union invaded.
Then they sent men and arms to oppose it.
Funny thing, in the Federalist papers, Madison and others belittled the idea that the militias of some states would send their armies to subdue other states. Turns out the Federalists were absolutely wrong, and the anti-Federalists were absolutely right.
Thirdly, the absolute command of Congress over the militia may be destructive of public liberty; for under the guidance of an arbitrary government, they may be made the unwilling instruments of tyranny. The militia of Pennsylvania may be marched to New England or Virginia to quell an insurrection occasioned by the most galling oppression, and aided by the standing army, they will no doubt be successful in subduing their liberty and independency. But in so doing, although the magnanimity of their minds will be extinguished, yet the meaner passions of resentment and revenge will be increased, and these in turn will be the ready and obedient instruments of despotism to enslave the others; and that with an irritated vengeance. Thus may the militia be made the instruments of crushing the last efforts of expiring liberty, of riveting the chains of despotism on their fellow-citizens, and on one another. This power can be exercised not only without violating the Constitution, but in strict conformity with it; it is calculated for this express purpose, and will doubtless be executed accordingly.
Prophetic.