Trade and Geography in the Spread of Islam.

In this study we explore the historical determinants of contemporary Muslim representation. Motivated by a plethora of case studies and historical accounts among Islamicists stressing the role of trade for the adoption of Islam, we construct detailed data on pre-Islamic trade routes, harbors, and ports to determine the empirical regularity of this argument. Our analysis - conducted across countries and across ethnic groups within countries - establishes that proximity to the pre-600 CE trade network is a robust predictor of today's Muslim adherence in the Old World. We also show that Islam spread successfully in regions that are ecologically similar to the birthplace of the religion, the Arabian Peninsula. Namely, territories characterized by a large share of arid and semiarid regions dotted with few pockets of fertile land are more likely to host Muslim communities. We discuss the various mechanisms that may give rise to the observed pattern.