I literally don't have any exact answers, so dm me or smth if this is wrong with A B C D or smth, but here:
During reconstruction, former confederate generals were unsupportive and extremely racist. Northern troops had to be sent to the south to enforce new anti-racist laws and delay the forming of Black Codes and Jim Crow laws. But still, The Ku Klux Klan formed, and Black Codes and Jim Crow laws formed with it once northern troops were sent away.