Under what conditions does religion become a salient social identity? By measuring religious attachment among the people living astride the Burkina Faso–Côte d’Ivoire border in West Africa, an arbitrary boundary that exposes otherwise similar individuals to different political contexts, this article makes a case for the importance of the political environment in affecting the weight that people attach to their religious identities. After ruling out explanations rooted in the proportion of different religious denominations, the degree of secularization and the supply of religious institutions on either side of the border, as well as differences in the degree of religious pluralism at the national level, it highlights the greater exposure of Ivorian respondents to the politicization of religion during Côte d’Ivoire’s recent civil conflict. Methodologically, the study demonstrates the power – and challenges – of exploiting Africa’s arbitrary borders as a source of causal leverage.

Africa’s arbitrary country borders have been seized upon as sources of “natural experiments”: having randomly assigned people to different country treatments, differences in outcomes on either side of the border can then be attributed to the institutions, demographics, or policies put in place in each country. While methodologically attractive, the use of African borders as sources of natural experiments presents several potential pitfalls. We describe these pitfalls—some common to all studies that employ jurisdictional boundaries, some unique to African borders—and offer guidelines for overcoming them. We conclude that African cross-border studies can provide research advantages similar to well-executed comparative case studies, but that they frequently offer weaker inferential leverage than is claimed.