Social Disorganization and Terrorist Attacks in the United States before and after 9/11

Despite much rhetoric regarding terrorism in recent years, little empirical research has examined patterns and predictors of terrorist attacks in the United States. We use newly available data on terrorist attacks in U.S. countries from 1990 to 2010 to test a set of hypotheses informed by a social disorganization framework.  Given the historic impact of the coordinated attacks of September 11, 2001, we also examine whether the determinants of terrorism changed after this iconic event. In particular, we hypothesize that the unprecedented increase in anti-terrorism policing following 9/11 not only reduced terrorist attacks but also produced the greatest reductions in terrorism in communities where policing is traditionally most successful—those with low population heterogeneity. Across the two decades spanned by the data, results show that terrorist attacks were more common in counties characterized by greater language diversity, a higher proportion of foreign born residents and greater residential instability. Moreover, while total attacks declined significantly after the 9/11 attacks, results show that the decline was less dramatic in areas characterized by high levels of population heterogeneity. We discuss the implications of the results for theory, future research and policy.