Ever read the Declarations of Secession? It was all about slavery. If you support that Democrat cause you're a pro-slaver.
I might suggest “The Cornerstone Speech” by The Vice President of the Confederacy, Alexander Stephens. In it he pretty much states that the “cornerstone” of the Confederacy is the inferiority of the black. That “platform” of the Confederation of Slave Power gained full traction following the Dred Scott decision made by the Supreme Court in the country’s first instance of judicial tyranny.