The Dynamics of Religious Conversion: Theory and Evidence

We develop a theoretical model of religious conversion in which potential adherents face changing payoff structures, spiritual or instrumental, triggered by the arrival of a new religious movement, the conversion of monarchs, or other shocks that alter the relative returns to conversion. Coupled with non-linear private returns in the share of co-religionists and intergenerational transmission of religious beliefs, our model yields multiple, stable steady-states in the community’s religious composition. We use this model to rationalize the spread of Islam in West Africa post-1500. The Atlantic slave trade altered payoffs in favor of Islam because Muslim rulers offered a de facto protection from enslavement, but only to their co-religionists. This created strong incentives for conversion among non-Muslims in regions exposed to slave raiding. Using newly compiled historical data alongside contemporary survey-based measures of Islamic presence, we show that communities under Islamic rule during 1500-1900 and exposed to Atlantic slavery exhibit persistently higher Muslim presence both after the end of slavery and today.