China is Not the New Rome: An Agent-Based Model Test of the Supply-Side Theory

Nationally representative surveys suggest Chinese Christian growth has plateaued at 2–5%, contrasting with supply-side predictions of 7–10% annual growth and an eventual Christian majority. Using an agent-based model, I formalize the theory's core mechanisms, including competitive evangelism, strict-church retention, cross-religion recruitment, and persecution-driven solidarity, under conditions more favorable to Christianity than any real religious market. Four findings emerge. First, the distribution of religious demand, not supply-side mechanisms, determines growth: under a neutral population, Christianity never exceeds 3%. Second, regulation always suppresses growth; the solidarity effect filters the church but does not grow it, consistent with historians' finding that Rome's Christian majority resulted from imperial patronage, not persecution. Third, strict churches win internal competition but cannot expand the convertible pool. Fourth, when declining intergenerational transmission is incorporated, the model's equilibrium falls to 4–5%, bracketing survey estimates. The debate over Chinese Christian numbers is not a data problem but a theoretical one: the theory's verbal predictions outrun what its own formalized logic can support.