David Kilcullen, president and CEO of the research firm Cordillera and a senior fellow at New America, is a renowned counterinsurgency theorist and practitioner. He served for 24 years as a soldier, diplomat, and policy advisor to the Australian and United States governments in contexts spanning Afghanistan, Iraq, East Timor, and Papua New Guinea. He is the author of four books, The Accidental Guerrilla, Counterinsurgency, Out of the Mountains, and Blood Year. In 2009, he was selected as one of Foreign Policy magazine’s Top 100 Global Thinkers. In October, he spoke to Diwan about Al-Qaeda, the rise and fall of the Islamic State, and what can be done about the enduring global terrorism threat.