You never studied American history have you.
One, slavery was an indirect cause of the war. The south was fighting for states rights, not slavery. They were fighting for their way of life, hundreds of years of doing one way, then the north comes along and says no, you have to do it this way, and no we will no compensate you.
Sumpter was far from "defenseless" and the North, through Abraham Lincoln, another over rated president, was gearing up for a war whether the south wanted it or not. Like all wars, the primary ingredient was greed.
But you know, other countries have had civil wars, uprisings, even Canada had the Upper Canada Rebellion in 1837. The difference is other countries get over them.