The Ku Klux Klan was a white supremacist movement that originated in the Southern United States after the Civil War. It was founded in 1865 and went through three distinct periods of activity. The KKK used terrorism, including violence and murder, to intimidate African Americans and promote their agenda of racist ideology. Over time their membership declined due to internal conflicts and opposition from civil rights activists like Martin Luther King Jr., though some KKK groups still exist today with only a few thousand members.