> The last time we tried that ...
Let's keep things in perspective here. Yes, the rest of the world was too complacent about the rise of the Nazis and Hitler, but that's not the last time we've had to deal with this sort of thing.
Red Army Faction (and Baader-Meinhof), Action Directe, the PIRA, the Corleonesi faction of the Sicilian Mafia, the FSLN, and the Basque ETA are all terrorist groups that essentially no longer exist or have mutated into legitimate political parties.
Still more recently than Hitler was neo-Nazism, which, while it still exists in pockets, has lost almost all of the coordinated criminal/terrorist organizations which existed in post-war Europe.
Suggesting that the narrative of ideological warfare went from the Crusades to WWII to ISIS with no breaks in between and meriting only a single response (military action) is historically naive.