Most ominously, the Denmark Vesey Conspiracy in Charleston in 1822 intended a general slaughter of whites before the conspirators would take to ships in Charleston harbor to sail away to the free black republic in Haiti. Many of the conspirators were relatively well-treated, trusted, and well-thought of by their white owners and associates, so the Denmark Vesey Conspiracy and the nihilistic violence it intended deeply unsettled the South.
A larger point also deserves mention. The South's fearful unwillingness to think about and discuss slavery and its evils discouraged Southerners against efforts toward reform or abolition. Had such a discussion been had, slavery might have mitigated and abolished gradually on terms that would have been far better than the devastation of the Civil War.
Trouble is, we've all been misled as to what was the purpose of the civil war. The South could have kept all of it's slaves so long as it agreed to keep sending all that money to the North.
The Passage of the Corwin Amendment by a 2/3rds majority in both the Republican controlled house and Senate shows that slavery was no obstacle to a continuing future in the "Union."
What the war was about was the fact the South was going to stop sending so much money into the pockets of the Northern industries. They were going to manage their own trade themselves, and thereby *KEEP* the lion's share of the profits, unlike what they had in 1860.
The Union government would tolerate permanent slavery, but it was never going to allow them to stop pumping money into Washington DC and the Northern corporate interests.
*THAT* is what the war was about.