It may not be possible to deter fanatical terrorists, but members of terrorist systems may be amenable to influence. The U.S. counterterrorism strategy should therefore include political warfare, placing at risk things the terrorists hold dear, a credible threat of force against states or groups that support acquisition of weapons of mass destruction, and maintaining cooperation with other nations engaged in the war on terror, while also preserving core American values.

This monograph summarizes the findings of a six-month project on deterrence of terrorism conducted jointly by RAND and the Institute for Defense Analyses (IDA). This study was initiated by a request to develop a framework for deterring terrorism. It was subsequently broadened to address, which greatly increased the operating space for our research, allowing us to consider measures ranging from co-optation to full-scale military attacks executed to deter future terrorist attacks (by al Qaeda or by others). This broadening of the problem also reflected a lesson gleaned from reviewing historical experience with terrorism: Successful strategies to combat terrorism spawned by serious, deep-rooted problems have involved first crushing the current threat and then bringing about changes to make terrorism's reemergence less likely. Thus, although concepts such as co-optation and inducement are not effective for dealing with terrorists who have the unshakable commitment of a bin Laden, they do apply to others that the United States must try to influence.

During the Cold War, deterrence theory was the cornerstone of U.S. foreign policy. Following the 9/11 terrorist attacks, however, popular wisdom dictated that terrorist organizations and radical fanatics could not be deterred—and governments shifted their attention to combating terrorism rather than deterring it. This book challenges that prevailing assumption and offers insight as to when and where terrorism can be deterred. It first identifies how and where theories of deterrence apply to counterterrorism, highlighting how traditional and less-traditional notions of deterrence can be applied to evolving terrorist threats. It then applies these theoretical propositions to real-world threats to establish the role deterrence has within a dynamic counterterrorism strategy—and to identify how metrics can be created for measuring the success of terrorism deterrence strategies. In sum, it provides a foundation for developing effective counterterrorism policies to help states contain or curtail the terrorism challenges they face.

Deterrence--a central feature of counterterrorism security systems and a major factor in the cost-effectiveness of many security programs--is not well understood or measured. This paper offers a framework for understanding how security systems may deter or displace attacks and how to measure the relative deterrent value of alternative systems. This framework may aid in attempts to achieve increased security benefits with limited resources.

Deterring terrorism is best approached as part of a broad effort to influence all elements of a terrorist system, and simple, conceptual models of decisionmaking can help in understanding how to affect others' behavior. The paper lays out a theory of how to use influence to affect elements of a terrorist system, touching on root causes, individual motivation, public support, and likely factors in the decisionmaking of terrorist organizations.

This book examines the question of how to deter a non-state terrorist actor. Can terrorism be deterred? This book argues that current research is unable to find strong cases of deterrence success, because it uses a flawed research design which does not capture the longitudinal dynamics of the process. So far, the focus of inquiry has been on the tactical elements of a state’s counterterrorism strategy, instead of the non-state actor’s grand strategies. By studying the campaigns of Hezbollah, the Palestinians, the Irish Republican Army, Chechens, the Kurdistan Workers' Party, and Al-Qaeda/Taliban and ISIS over time, we can see that deterrence strategies that target the cost-benefit calculus of terrorist organizations lead to wars of attrition – which is the non-state organization’s strategy for victory. To escape the attrition trap, the state must undermine the attrition strategy of terrorist organizations by using offensive campaigns that become critical educational moments. The case studies presented here uncover an evolutionary process of learning, leading to strategic deterrence successes. Some terrorist organizations abandoned the use of force altogether, while others abandoned their aspirational goals or resorted to lower levels of violence. These findings should enable policymakers to transition from the failed policy that sought to defeat the Taliban and al-Qaeda in the unending war in Afghanistan to a policy that successfully applies deterrence. This book will be of much interest to students of deterrence theory, terrorism studies, war and conflict studies, and security studies.