Prebisch, former head of Argentina's Central Bank, saw the world as two distinct areas: a center of economic power in Europe and the United States and a periphery of weaker countries in Latin America, Africa and Asia. Prebisch concluded that Latin America's underdevelopment was due to its importance on primary exports. The periphery was underdeveloped because it needed to create more livelihood and raw materials for export in order to import a specific amount of industrial imports. Andre Gunder Frank argued that external monopoly led to foreign expropriation, and therefore local unavailability, of a significant portion of the economic surplus actually produced in Latin America. Therefore, the region was actively underdeveloped by not generating to its potential and losing its surplus to Europe and North America. Peripheral countries were prevented from achieving development because they sold their products at prices below their value, while rich countries sold products at prices above their value (Peet and Hartwick pp. 188-199). Therefore, in contrast to modernization theory, which emphasized the benefits of free trade, foreign investment, and foreign aid, these theorists argued that free trade and the international market