The South left the Union in order to defend slavery and racial supremacy. The Southerners believed it was a scientific truth of the world that blacks were inferior and should be subservient. They didn’t lose these beliefs the moment they lost the war. After the Civil War, White Southerns responded to the loss by organizing in order to persecute, murder, beat, and instill fear in, blacks, in order to keep them down and maintain racial supremacy. White Southerners maintained white supremacy through terrorism.
The Klu Klux Klan, the KKK, started as a kind of social club, almost like a college fraternity. They made up silly-sounding titles and wore fun costumes. The people in it were racists, but they didn’t set up the organization to do racist things.
The Klan became a political organization when members perceived the North’s rule as too aggressive in potentially arming blacks in state militias and giving them the ability to vote.