The truth was the KKK was against a lot of people, Irish, Catholics, Germans, etc. Their operational center was in Indiana.
They didn't burn crosses until the movie came out. The movie needed a light source to film at night and someone thought burning crosses would be a good idea. The KKK started doing this AFTER they saw the movie.
I grew up in NW Iowa and my Dad told me a story about coming home one night in the early 30’s and the yard was full of KKK and a cross was burning on the hill side. I asked my Dad why they would do that, there weren't any blacks in town. He said “yeah, but there were catholics.” It was a different time and place.
Not only those people but they also went after anyone who dared vote republican too.The letters are included in the national archives of southern republican begging for the government to send troops to stop the KKK.
My mother in law told my children(for a family history project) that when we she was a kid, her family went to KKK rallies in Kansas and it was against Catholics not blacks. She said she was around 10 so that would have been in the late ‘20’s- early ‘30’s.