Demography drives religious change. That bald comment is too obvious to be worth making, but it’s surprising how little attention demographic factors receive in most histories of religion, particularly of Christianity. That neglect means we miss a very large part of the story.
Given a sufficiently high birth rate, a minority religious community can rapidly be come a dominant majority, with all that implies for distributing social power and shaping conflict. Alterna tively, migration can transform the religious economy of a hitherto static society.
Demographics also shape the prevailing forms of religion. A country with a marked youth bulge—with lots of adolescents and young adults—is far more open to explosive revivalism than a more sedate and middle-aged society. Changing demographics can also have a pastoral impact, revolutionizing perceptions of childhood and old age. Numbers may not be everything, but they certainly are something.