Sooner or later, we will have to come to the realization that terrorism cannot be eliminated by force. Stop destabilizing Arab countries, stop imperial interference in Northern Africa, and perhaps we'll see an end to this nonsense.
If there's any lesson from the past 15 years, it is this: state engineering does not work. Period. You cannot control it. You don't "allow" anything. You cannot stop anything. The forces are beyond your control.
Americans and Europeans have to step out of the colonial mindset of trying to control the world. Then we'll have peace.