The document discusses several theories of international trade, including mercantilism where a nation has a monopoly on a product, absolute advantage where a nation can produce something at the lowest cost, comparative advantage where a country can produce a good at a lower opportunity cost, the Heckscher-Ohlin model where capital-abundant countries export capital-intensive goods and labor-abundant countries export labor-intensive goods, product cycle theory where production moves away from the point of origin, Linder's theory where countries trade more if their demand structures are similar, Krugman's model of national specialization by industry, and the Diamond of National Advantage about creating new advanced factors rather than relying on natural competitive advantage.