In any situation like this, you absolutely must have spies inside the organization ratting them out. You can then start thinking about military strikes, assassinations, etc. Whoever said you can't kill a belief was absolutely correct. With the proper intelligence, you can drive the believers far enough underground that they no longer present a serious threat. It requires a good deal of ruthlessness. For examples, study how the Brits dealt with the Thugee cult, the Nazis dealt with partisans, and the Soviets dealt with dissident organizations. I hasten to add that I don't want us to become like the Nazis or Soviets, I am simply stating that when you are trying to deal with amorphous terrorist cells, you don't win by playing nice. Their people can be "turned" lots of ways...bribery, terror, fear for safety of their own loved ones, etc.