An expanded unified growth theory that includes endogenous accumulation of physical capital, population, human capital, and technology is described here. The model depicts how physical and human capital complement each other in a multi-country setting with global technological dissemination. Current findings are explained by long-term growth and comparative development. Numerical multi-country models replicate long-term growth and comparative development. Demographic shift impacts convergence patterns, cross-country growth regressions, technology spillovers, and secular stagnation.

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