The Classical Trade Theory or simply the Ricardian Model assumes that comparative advantage of the countries solely depends on the relative differences in the productivity of labor. Nevertheless, it does not explain the reason of these productivity differences. In other words, the Ricardian Model does not clarify the basis of the comparative advantage. Heckscher-Ohlin Theory was developed so as to respond to two questions that had not been answered by the Classical Trade Theory: (1) What is the determinant of the comparative advantage of the countries? (2) How does international trade affect the earnings of the factors of production within the trading countries?