We show that even in the absence of diminishing returns in production and technological spillovers, international trade leads to a stable world income distribution. This is because specialization and trade introduce de facto diminishing returns: Countries that accumulate capital faster than average experience declining export prices, depressing the rate of return to capital and discouraging further accumulation. Because of constant returns to capital accumulation at the country level, the cross-sectional behavior of the world economy is similar to that of existing exogenous growth models: Cross-country variation in economic policies, savings, and technology translate into cross-country variation in incomes, and country dynamics exhibit conditional convergence as in the Solow-Ramsey model. The dispersion of the world income distribution is determined by the forces that shape the strength of the terms of trade-effects--the degree of openness to international trade and the extent of specialization. Finally, we provide evidence that those countries accumulating faster experience a worsening in their terms of trade. Our estimates imply that, all else equal, a 1 percentage point faster growth is associated with approximately a 0.7 percentage point deline in the terms of trade.