With its fiery crosses and nightriders in pointed hoods and flowing robes, the Ku Klux Klan remains a recurring nightmare in American life. What began in the earliest post-Civil War days as a social group engaging in drunken hijinks at the expense of perceived inferiors soon turned into a murderous paramilitary organization determined to resist the evils of radical Reconstruction. For six generations and counting, the Klan has inflicted misery and death on countless victims nationwide and since the early 1920s, has expanded into distant corners of the globe. From the Klan's post-Civil War...