Answer:
12, the Missouri compromise
11, Nat Turner's rebellion
10, Wilmot proviso
9, the compromise of 1850
8, uncle toms cabin
7, bleeding Kansas
6, Dred Scott
5, Lincoln/Douglas debates
4, john browns raid
3, Slavery
2, Lincoln election
1, FT.Sumter
I think this is how it goes, hope it's right good luck