I don't see where I'm wrong - southern leaders had made slavery an issue for years, and in 1850 made it explicitly a federal issue by demanding a federal remedy for fugitive slaves. There's nothing very startling about that.

I agree that laws on the books should be enforced (unless they are silly or morally repugnant). I will leave aside the argument that defying slave law was justifiable civil disobedience and agree that, in the context of that time, it was not unreasonable for southern slave-owners to seek a federal remedy. I just enjoy the irony of that.

"...let's just say that 10% of the South were slave owners. Is that enough slave owners to start a war?" Given that it was the largest and most powerful slave-owners who led the secession movement, I'd say it is entirely possible that 10% of the population can "start a war" - but not to hold out for four years. That takes many more. I would argue that the wives, children, other kin, employees, etc. of those slaveowners were as invested as the owners were in the slave system - not to mention the many thousands of non-slaveowners who hoped to rise to the social and economic status of slaveowners someday.