Repatriation. It’s why Lincoln had to die.
In the election of 1864, George B. McClellan (D) ran against Lincoln on a platform of ending the Civil War by armistice with the Confederacy, readmission of the South into the Union, ending slavery and repatriation to Africa of all southern black slaves, incrementally, by 1900. This would have given the South 35 years to close out slavery without completely destroying their economy, and it would have allowed the South to free their slaves without then having to live side by side with them which was what Southern whites wanted more than anything.
What a different country we would now have if McClellan had of won that election, and some say he really did.