Abrahms marshalls quite a bit of evidence for his points. Fascinating read, from International Security.
Abrahms has an alternative model to explain all this: People turn to terrorism for social solidarity. He theorizes that people join terrorist organizations worldwide in order to be part of a community, much like the reason inner-city youths join gangs in the United States.HT: Carl at No Oil For Pacifists.
The evidence supports this. Individual terrorists often have no prior involvement with a group's political agenda, and often join multiple terrorist groups with incompatible platforms. Individuals who join terrorist groups are frequently not oppressed in any way, and often can't describe the political goals of their organizations. People who join terrorist groups most often have friends or relatives who are members of the group, and the great majority of terrorist are socially isolated: unmarried young men or widowed women who weren't working prior to joining. These things are true for members of terrorist groups as diverse as the IRA and al-Qaida.
For example, several of the 9/11 hijackers planned to fight in Chechnya, but they didn't have the right paperwork so they attacked America instead