War between the States...
Well it goes back further than that:
"Black Republicans
From 1854, when the Republican Party was founded, Democrats labeled it adherents "black" Republicans to identify them as proponents of black equality. During the 1860 elections Southern Democrats used the term derisively to press their belief that Abraham Lincoln's victory would incite slave rebellions in the South and lead to widespread miscegenation. The image the term conveyed became more hated in the South during Reconstruction as Radical Republicans forced legislation repugnant to Southerners and installed Northern Republicans or Unionists in the governments of the former Confederate states."
I read the Civil War was fought because of the Dred Scott decision.
Before that the North and South had the Missouri Compromise and a gentleman's agreement.
But the decison by SCOTUS didn't just declare that slaves were "property" that could be "recovered", meaning slave holders could go into the North and get runaways, it also meant that slave holders could move North and bring their slaves with them.