Protip: You can quibble abou states' rights and tyranny and blah blah blah, but the American Civil War was fought over Slavery. Hurkendur.
The South was locked with the North over "Free soil" legislature, and threats of secession were increasingly common to protest their passage. When California became a state in 1850 with overwhelming support for being a "free state," the balance tipped to the free states' favor at last. From this point on, tensions increased dramatically and fights broke out in congress resulting in serious injuries. Before the civil war, there was a lot of civil strife in the Kansas-Nebraska territories, among other places, over precisely the issue of slavery.
Only an ignorant fool can say the Civil War wasn't about slavery. Sure, there were other factors, but without them the Civil War would have still likely taken place. Without the issue of slavery dividing the country, it never would have happened.
Dumb ass.