People join violent groups for a variety of reasons, and they differ in their levels of commitment. Brain scans offer new insights into a particular type of members, the backbone of these groups we call “devoted actors.”
Opportunities to meet a caliph are pretty rare. Yet in London in the 1990s, you could bump into a protector of the entire Muslim world on the Central line. He wore no finery, of course, and his palace was a two-bedroom government apartment in Dagenham.