Terrorism and Irregular Warfare

The CSIS Warfare, Irregular Threats, and Terrorism Program collaborates with the International Security Program, Middle East Program, Africa Program, and more to provide analysis on irregular and hybrid warfare, terrorist violence, and military operations. 

Photo: ED JONES/AFP/Getty Images

Photo: ED JONES/AFP/Getty Images

Adapting to the New Terrorism Landscape 25 Years After 9/11

Post-9/11 counterterrorism efforts made large, foreign-directed attacks harder to execute. Stopping the terrorist threat that remains today requires a new approach.

Commentary by Riley McCabe — September 10, 2026

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Daniel Byman

Daniel Byman

Director, Warfare, Irregular Threats, and Terrorism Program
Seth G. Jones

Seth G. Jones

President, Defense and Security Department; Harold Brown Chair
Jon Alterman

Jon B. Alterman

Zbigniew Brzezinski Chair in Global Security and Geostrategy

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The Last Line of Defense

25 Years After 9/11: Is America Prepared for the Next Crisis?

Host Dr. Seth Jones sits down with Dr. Dan Byman, director of the Warfare, Irregular Threats, and Terrorism Program at CSIS and professor at Georgetown University's School of Foreign Service, to mark the twenty-fifth anniversary of the terrorist attacks of September 11, 2001.

Podcast Episode by Seth G. Jones and Daniel Byman — September 11, 2026

The Last Line of Defence

Artificial Intelligence and the Future of Terrorism

AI will not transform terrorism overnight. Its more likely effect is subtler: lowering barriers for extremist propaganda, recruitment, disinformation, and planning while strengthening counterterrorism tools and surveillance risks.

Brief by Daniel Byman and V.S. Subrahmanian — July 10, 2026

The War May Be Ending. What Did Epic Fury Cost?

Iran war costs are estimated to be between $34 billion and $42 billion. As neither the FY 2026 defense budget nor the FY 2027 budget request includes war costs, Congress faces a major battle over paying for the war.

Report by Mark F. Cancian and Chris H. Park — June 23, 2026

The Terrorist Threat to the 2026 World Cup

The 2026 World Cup will be the largest sporting event ever held and a magnet for terrorists of all stripes. A new CSIS brief examines who might attack, what targets are at greatest risk, and the countermeasures being deployed.

Brief by Daniel Byman and Riley McCabe — May 27, 2026

Global Terrorism Threat Assessment 2026

Terrorism is currently declining as a U.S. national security priority, and resources available for counterterrorism are decreasing accordingly. At the same time, uncertainty regarding the future of global terrorism is increasing, bringing greater risk of surprise.

Report by CSIS Scholars — May 26, 2026

The Many Faces of Antisemitic Terrorism in the United States

Anti-Jewish violence in America is no longer driven by one ideology alone. Neo-Nazis, jihadists, anti-Israel extremists, and even state-backed actors are converging on the same targets, stretching counterterrorism defenses and redefining domestic security threats.

Commentary by Daniel Byman — May 26, 2026