Salafi extremism, embraced by organizations such as the Islamic State, is a global religion-invoking phenomenon whose primary cause is not clearly elucidated in the literature. Unlike most existing models or explanations of terrorism that attempt to explain stages or factors associated with the radicalization of individuals, this study aims to identify the dominant causal pathway behind the onset of Salafi extremism. The independent and dependent variables and the variable associated with the causal pathway invoked here are public support levels for religious leaders as religious judges, the radical agenda they espouse, and the idea of Sharia as the law of the land, respectively. A linear regression analysis of the observational data from 20 nations revealed that the Sharia platform acts as both a causal mediator and moderator vis-à-vis the independent and dependent variables. The use of Kosovo as the control in this study minimizes or eliminates confounding bias, and the high magnitude of the computed coefficients of determination minimizes the contribution of any omitted variable. Thus, the preliminary conclusion is that the belief in Sharia as the law of the land, as advocated by religious leaders, provides the basis for radicalization and the emergence of Salafi jihadist groups.