Ryan Shaffer has a PhD in history with expertise in extremism and security. He has published hundreds of articles and reviews in numerous journals. His books include African Intelligence Services: Early Postcolonial and Contemporary Challenges and The Handbook of African Intelligence Cultures.

Jeffrey Kaplan is currently the Distinguished Fellow at the Danube Institute in Budapest and the External Expert at the Islamic Cultural, Educational, and Scientific Organization (ICESCO) in Rabat, Morocco. He is the author or editor of thirty books and anthologies and over 100 journal articles and anthology chapters. He has researched and taught in many countries, most recently Hungary, China, Saudi Arabia, and Pakistan.

Introduction-The legacy of 9/11: a retrospective 1. Twenty years of countering jihadism in Western Europe: from the shock of 9/11 to 'jihadism fatigue' 2. From 9/11 to the POST Act: democratic oversight of police surveillance technologies in New York City 3. How we went from 9/11 to lone actors 4. 9/11's legacy of unintended consequences 5. The analytic challenges of shifting to domestic terrorism 6. The expansion of the transnational counterterrorism order after 9/11 7. Homegrown tribalism: would-be al-Qaeda subway bombers and an ISIS defector 8. A world remade: 9/11, America and the western world