Back to the Civil War. I'm reading "The Clansman"...the book that was the basis for "Birth of a Nation".
So, anyway, here is what Wiki says was the motivation of the author to write the story:
Dixon wrote The Clansman as a message to Northerners to maintain racial segregation, as the work claimed that blacks when free would turn savage and violent, committing crimes such as murder, rape and robbery far out of proportion to their percentage of the population.
