Back then, the Republican Party was still the Party of Lincoln, and Republicans primarily represented Northern industrialists. Northern Industry is the main reason the North won the Civil War. Hard to find a more hated combination in the South. Democrats were populists, representing farmers and working men.
As the young were added to the voting roles, that old difference started to change. The final straw was LBJ's Civil Rights Act and Nixon's Southern Strategy. The Republican Party's connection to the rich was downplayed (although still ever-present) and the racial divide used to drive racists into the Republican Party. Not every White person in the South was racist by any means (at least not for those times), but there were enough.
