The work of Understanding Terror Networks author Marc Sageman is featured in Azzam the American: The making of an Al Qaeda homegrown, a recent New Yorker article about jihadism in the United States.
New Yorker reporter Raffi Khatchadourian tells how Sageman, a forensic psychiatrist and former C.I.A. case officer, examined the available data on a hundred and seventy-two jihadists and found that factors such as poverty, past mental illness, criminal record, and brainwashing had little to do with their militancy. Khatchadourian writes:
Perhaps his most unexpected conclusion was that ideology and political grievances played a minimal role during the initial stages of enlistment. “The only significant finding was that the future terrorists felt isolated, lonely, and emotionally alienated,” Sageman told the September 11th Commission in 2003, during a debriefing about his research. These lost men would congregate at mosques and find others like them. Eventually, they would move into apartments near their mosques and build friendships around their faith and its obligations. He has called his model the “halal theory of terrorism”—since bonds were often formed while sharing halal meals—or the “bunch of guys” theory. The bunch of guys constituted a closed society that provided a sense of meaning that did not exist in the larger world.
The complete article is available at www.newyorker.com.
The "bunch of guys" theory and other models of terrorist behavior are detailed in Understanding Terror Networks.