Every state had legal slavery in 1776. Presumably God would have objected just as much then as he would in 1861, yet the US won independence from Britain none the less.
I know that if you had asked a Northern soldier in 1861 why he was fighting, he would have told you "because they attacked Ft Sumter." If you had asked a Southern soldier in 1861 why they were fighting, he would have replied "Because they invaded our homeland."
I don't think "Slavery" was much of a consideration for either one of them until much later in the war.
No. Apart from the fact that there weren't any states in 1776, Rhode Island had banned it in 1652. First colony to do so. Also, at the time, the biggest importer of slaves. There's a bit of history trivia for you.
No, from the beginning most Northern citizens understood that preserving the Union was at stake, but the question for months was: would secession start war?
And the answer was always: no, so long as Confederates don't start it, there will be no war.
That's what Lincoln's First Inaugural Address said.
What Fort Sumter did was clearly, unequivocally start the war.
Confederates began the war as an effort to assert their sovereignty over all Federal properties, especially Fort Sumter, and in the firm belief that Southern "manliness" would quickly & easily defeat those effete "Dough-faced" Northerners.
Remember, when Confederates began the bombardment of Fort Sumter, on April 12, 1861, their Army was authorized at 100,000 troops, quickly volunteered for, while the entire US Army totaled around 16,000 mostly scattered in forts out west.
Further, most Union generals were not overly enthusiastic about a war against their Southern class-mates.
So there was no big reason for Deep-South Fire Eaters to think that a "glorious war" would result in their utter defeat and destruction.