"I think a fair indicator of what its scope is and what it will someday be is simply to reflect on the journey we have taken with Sunni violent extremism, which of course is only one form of terrorism. On 9/11, the dominant Sunni extremist actor, which was al-Qa`ida, existed in essentially four places: Afghanistan, Pakistan, Yemen, and the Sudan. Where is it today? The answer is not reassuring. That is probably an instructive trajectory to consider when one asks the question, “Where will it be in the next 10 years?” It will probably be more expansive than it is today. And when you have this very unusual phenomenon of the Islamic State, I actually don’t think it’s a linear slope, and we must ensure it does not become exponential in nature."