Why do racist/populist movements spring up years or decades after the event(s) they're tied to?

For example, why did the KKK come to prominence 30 years after the Civil War ended, and again in the 1920s, and why did the Nazis gain so much traction after the German economy was starting to recover?

(More examples would be awesome, but I'm really interested in academic research/articles about why this sort of delayed-effect phenomenon happens in the first place!)