So what causes were the biggest causes?

1. Election of 1860: Southerners really feared for their rights to slavery when Lincoln was elected, and were furious when he won despite the votes of nearly the entire South going to Breckenridge. They feared that he would only advocate for Northern states and despite his offers of non extension, not abolishment, of slavery, his election was the trigger that caused the Secession of the first wave of Southern states.

2. Bleeding Kansas: It was the first outright bloodshed and killing between whites over slavery. The settlers in Kansas turned against their neighbors to gain an advantage for their cause, a chilling precedent for what was to come during the Civil War, when brothers fought brothers and families were shooting at each other from opposite sides of a field.

3. John Brown's Raid on Harpers Ferry: An attempt to arm slaves against their masters was a cause for alarm in the South where slaves usually comprised more than a third of the population, or even outnumbered whites. Not only did this create hostilities against meddling Northern abolitionists, in the North John Brown's martyrdom became a rallying point for the crusade against slavery.

4. Uncle Tom's Cabin: The book led to outrage on behalf of slaves in the North, strengthening the abolitionist cause while creating anger in the South at the "lies" told in the book. Those sympathetic to the abolitionist cause, or at least open to it, couldn't escape the humanity that blacks were portrayed to have. They were just like whites.

5. Dred Scott vs. Sanford: In comparison to Uncle Tom's Cabin, the Supreme Court declared blacks to be inferior to whites and unsuitable for society. It also alarmed Northerners by implying that since Scott's master was able to take him to Illinois, a free state, no state could ever be truly slavery exclusive.

6. Kansas-Nebraska Act: The cause of Bleeding Kansas, popular sovereignty was a dismal failure that resulted in chaos, the formation of multiple simultaneous state governments, and open conflict between North and South, a piece of legislature mostly thought up in order to avoid taking a stand and offending someone.