For much of the twentieth century, it was widely believed that the march of modernity—industrial growth, scientific progress, and democratic governance would steadily push religion out of public life. Sociologists called this the secularisation thesis: as societies advanced, religion would retreat into private belief, losing its grip on politics and institutions. For decades, this seemed plausible in parts of Europe and North America. Yet by the turn of the millennium, it was clear that this story had been oversimplified....