Next I suppose you'll be telling us that Islam is a religion of peace.
Let us suppose that slavery was indeed a minor issue in the civil war. Why did the South secede, then? (And why did slavery figure so prominently in those wily Southerners' Declarations of Secession?)
The southern states were paying 90% of the taxes, and had 10% of the population, thus no hope of correcting the problem.
What was featured in South Carolina's declaration was not slavery but the failure of the north to enforce the provision in the Constitution requiring the return of fugitive slaves. In other words, we didn't break the compact, you did.