I learned about this from listening to The History of the United States
The South lost the Civil War, that made Slavery illegal. But it retained most of the same social dominance, of Whites over Blacks – that existed before the War. And it resisted these reforms violently – in large sections of the South, no one dared vote as a Republican – the party determined to reform the South.
It wouldn’t be until LBJ (a Democrat) and his Civil Rights reforms (a century later) – that these reforms would finally take place.