US democracy also survived the rise of the KKK, courtesy of very strong free speech and free press protections. Had the US lacked such, it's entirely plausible that the KKK could have become the US version of the National Socialists in Germany. I think a lot of people are ignorant of just threatening the KKK was for a few decades. The ability to freely argue ideas, and for the right ideas to win, is what made it possible to fundamentally neuter the KKK (such that now they're a meaningless, powerless, small group with no real impact on national politics). All of that was accomplished without having to fight a military conflict with the KKK / destroy them with force.
It seems to me that the KKK had about three stretches of considerable power: in the south during Reconstruction; in the south with some considerable influence in Pennsylvania, the Midwest, and as far as Colorado, during the 1920s; and again mostly in the south in the 1950s and 1960s.
After Reconstruction, the KKK essentially won--no black votes, no black officials. In the 1920s, I think it reduced itself to absurdity, with a high official jailed under the Mann Act. And law enforcement, notably the FBI, had a good deal to do with the end of its 1960s power.
