What are three events that occurred between 1857 and 1859 that facilitiated southern secession

I believe the 3 events where, The Lincoln-Douglas Debate, The john brown raid and the Dred Scott Verdict. Browns raid made abolitionist (against slavery) look as if they where the bad guys, Lincoln-Douglas Made each state decide if they wanted to be a slave or no slave state and the Dred Scott made slavery 'legal' anywhere in the U. S. A. Dred Scott was 1857, Lincoln-Douglas was 1858 and John Brown Raid was 1859!