  This paper compares networks of foreign fighters who joined the Islamic State
of Iraq and Syria (ISIS) from Europe and the Arabian Peninsula in order to test
whether there are differences in their recruitment and how those differences
affect the nature of the foreign fighter mobilization. It is the first study to
compare different networks of foreign fighters that joined the same group in
the same conflict at the same period of time. This study finds that foreign
fighter recruitment resembles an efficiency-secrecy tradeoff: in places where
recruitment needs to be hidden from legal scrutiny, recruitment networks are
decentralized; composed of small and more local recruitment cells. These cells
can operate more secretly and the group as a whole is more resilient to
disruption. In exchange, it is hard for the group to attract large numbers of
recruits. Whereas in places where recruitment could occur more freely,
recruitment networks are more hierarchical; comprised of a larger number of
recruits with more geographically diverse connections. The hierarchical design
of their recruitment networks may be easier to disrupt, but it also helps the
group efficiently recruit more followers if left undisturbed. This study
concludes that the ISIS foreign fighter recruitment process varied
significantly. Researchers and policymakers focused on recruitment and
radicalization should therefore carefully frame their results or policies based
on the different types of recruitment processes and the various social,
political, and legal contexts where their work takes place.
