Extremists of a Feather Flock Together? Community Structure and Patterns of Homophily in the US Islamist Co-Offending Network

Abstract

Violence is exacerbated in small close-knit groups and through social identi cation processes.Furthermore, the homophily principle postulates that individuals tend to form relationshipsbecause of shared characteristics. We analyze the community structure of the Islamist co-o endingnetwork { a highly violent social network { and assess whether shared characteristics increase theprobability to form co-o ending ties. We rely on a new database on the individual attributes andthe co-o ending relationships of 503 Islamist o enders radicalized in the United States between1948 and 2020. Using community detection algorithms, we show that the US Islamist co-o endingnetwork is highly clustered, modular, and includes only a few large communities. Furthermore,results from the exponential random graph modeling evidence the roles of spatial proximity,ideological a liation, and shared social characteristics in driving co-o ending among US Islamists.Overall, these ndings demonstrate that small, local communities and homophily shape violentsocial networks.