Freakonomics: Chapter 2

While World War II caused the Klan to lie low for a while, it revitalized strongly after the war, with its headquarters in the city of Atlanta. There, Stetson Kennedy, a writer who was dedicated to ending bigotry, decided to go undercover and join the Klan in order to reveal its coveted secrets that might help lead to its destruction. He wormed his way into their ranks, learning all their secret customs, and eventually was invited to join the Klavaliers, who were the Klan's secret police.

By this point, the Klan was a lot less violent than it used to be, and carried out many fewer lynchings; instead, the real power of the 1940s Klan was their fear rhetoric. Kennedy realized the best way to take the Klan down was to expose their secret information to the world in whatever way he could, so he fed these important Klan secrets to a radio show listened to which many children listened, called "Adventures of Superman." Once everyone knew all this information, it turned into a tool for mockery, and Klan membership fell drastically.