When denied their primary target, do terrorists strike elsewhere?

University Press Release

Criminals who are thwarted by situational crime prevention measures – such as increased security, fortifications or surveillance – may seek out more accessible if less appealing targets, known in criminologists’ parlance as “crime displacement.” Since 9/11, there’s been growing evidence that such prevention measures have been useful in thwarting opportunities for terrorist attacks on U.S. soil. But does this imply that terrorists, like other criminals, simply find other more vulnerable targets?  Not necessarily, says University of Houston-Clear Lake criminologist Henda Hsu in an article published in Justice Quarterly, a publication of the Academy of Criminal Justice Sciences.

Hsu, an assistant professor of criminology, collaborated with criminal justice colleagues Bob Edward Vasquez of Texas State University and David McDowall of State University of New York at Albany to write “A Time-Series Analysis of Terrorism: Intervention, Displacement, and Diffusion of Benefits.”

The article focuses on the extent to which the difficulty of planning domestic U.S. attacks has been displaced to attacks on U.S. targets abroad. “This paper discusses the perception that displacement in terrorism is inevitable; that antiterrorism efforts merely relocate terrorism in some way,” Hsu writes.

Crime displacement, the article explains, is the notion that crime prevention efforts are capable of relocating crime, but they cannot reduce or interrupt it. The most common presentation of crime displacement invokes a shift in the crime’s physical location.

But crime displacement is difficult to document and test for causal relationships, Hsu points out. “At the heart of crime displacement is relocation, indeed, but this ‘relocation’ can come in the form of a shift in place, time, target, nature, or a combination of these possibilities.”

Citing his own 2015 research, Hsu cautions that crime displacement should not be viewed as an inevitability. “Regardless of its plausibility and popularity, the limited evidence in support of crime displacement prevents displacement from being viewed as a well-established phenomenon.”

Using data from the Global Terrorism Database (1994–2013), the authors tested the hypothesis that target-hardening efforts within the U.S. after 9/11 have reduced attacks on domestic targets but have increased attacks on U.S. targets abroad. However, their analysis showed no support for the displacement hypothesis. Instead, it pointed to a “diffusion-of-benefits” hypothesis.

“Rather than generating subsequent increases in attacks directed at U.S. targets abroad, we see a consistent, and mutually-reinforced, decline in attacks for both series,” the authors write, but also take care not to overstate their case. “Although substantive, the accumulation of the reductive effects is short-lived. We note that the pattern of the findings could be much more convincing.

“Our findings provide encouragement for U.S. policymakers that Homeland Security efforts to safeguard the U.S. from terrorist attacks will not simply induce terrorists to attack U.S. targets and interests abroad. The larger point is that our results provide support to recent criminological arguments that pervasive fears about the sureness of terrorism displacement in the terrorism literature may be unwarranted.”

The research concludes that the displacement of terrorism is a complex phenomenon involving the terrorists’ immediate goals, preferences, and operational opportunities and constraints.

The article was also featured in the August newsletter of the Crime and Justice Research Alliance, a resource created to provide policymakers, practitioners and the public access to relevant research on crime and criminal justice issues.