This paper applies the infra-marginal analysis, which is a combination of marginal and total cost-benefit analysis, to a model with both constant returns and increasing returns in production and with exogenous and endogenous comparative advantages. It demonstrates that as transaction conditions are improved, the general equilibrium discontinuously jumps from autarky to partial division of labor with a dual structure, then to the complete division of labor where dual structure disappears. Two types of dual structure may occur in the transitional stage of economic development and globalization. One of them involves the division of labor in the developed economy and autarky in the less developed economy, generating increasing disparity of per ...