"aggressive racism wasn't really seen in the south before the Civil War" is absurd and only supportable if you don't consider the treatment of the slaves. There was a ton of brutality, and you're sitting here saying there wasn't any aggression.

It's not dissimilar to the US wars in the middle east: The North toppled an evil government, freed some people, but didn't finish the job. So assholes ended back up in charge. They couldn't go quite as far, or quite go all ISIS, they had to settle for just the KKK, because it was all one country again, but somehow the losers didn't lose all that much in the long run.