In “The Extremist's Advantage in Civil Wars,” Barbara Walter seeks to explain the rise of radical Islamist groups in civil wars since 2003, especially Salafist groups.1 She claims that ideologically extreme groups have an organizational edge and thus outperform more moderate groups. This thesis is unpersuasive, however, because of its shaky empirical basis.
Walter's core assumption is that an extreme ideology helps groups attract support. Her definition of ideology encompasses their political preferences and the tactics used to achieve them. As she states, ideology is “a set of beliefs about the proper order of society and how it can be achieved” (p. 15). Walter expresses skepticism, though, in rating the extremeness of groups based on their conduct, perhaps because of the mounting empirical research showing that moderate groups attract disproportionate support.2 Indeed, a common way for groups to end is by acting too extreme, as doing so dries...