How threatening are al-Qaeda and the Islamic State? In Jihadism Constrained,Barak Mendelsohn suggests that although jihadi terrorism is a serious challenge, it must not be exaggerated. Transnational terrorist organizations and jihadi transnational groups in particular face three central challenges: How to create a polity that is based on religious affiliation when most people identify with national and sub-national identities? How to generate political effects across borders? And how to produce unity among all components of the transnational movement? The book argues that transnational jihadism has been struggling on all three fronts. Success of armed nonstate actors hinges on their ability to mobilize the masses, but transnational jihadis persuaded only a tiny fraction of the world’s Muslims to abandon their other identity markers and support a faith-based global polity that promotes an extreme interpretation of Islam. As military pressure endangers cross-border activities, jihadi groups introduced local branches only to find that such localization undermines their transnational agenda. Jihadi groups also lack a viable plan to turn armed success in separate states into cross-border political effects. Finally, jihadis regularly fall into internal conflicts. These conflicts are exacerbated by the use of Islamic discourse that renders compromise and reconciliation particularly difficult.