Using criteria that she developed and elaborates, the author classifies rebel groups on a continuum from extreme to moderate. She shows that extreme Islamist groups were able to attract fighters away from initial moderate groups because they had better internal organization, took better care of fighters (physically and monetarily), and experienced less internal corruption. The author explains how extreme groups benefited from Islamist ideology, which helped ensure, among other things, that only the most dedicated fighters joined their ranks. However, one unforeseen side effect of using ideology as a central factor was attracting fighters more interested in Islamic ideology than fighting. With time, such individuals wasted group resources and caused internal splits and power struggles over the goals of the conflict. For ISIS, handling these issues became a major part of their decline.