Terrorism

But the real answer is that Europeans didn't just "put up with it" - they treated terrorists like the criminals they were and didn't allow them to completely disrupt their way of living. They did not suddenly get behind an excited drive to gut their treasuries and impoverish their countries and their people by setting off half-cocked on some stupid permanent state of war that would wipe out the very civil liberties and trust in law that made their nations worth living in to begin with.