Why do international economic theories all originate in the middle of18th century?

Because it appeared in the 65438+1940s.

Based on the general theory of economics, international economics studies international economic activities and international economic relations, which is the application and extension of general economic theory in the scope of international economic activities and an organic part of the economic system. The main research objects are international trade theory and policy, balance of payments theory, exchange rate theory, international factor flow, international investment theory, open macroeconomic equilibrium and so on. International economics was gradually developed on the basis of traditional international trade and international finance in the early 1920s. After World War II, it has been paid more and more attention in capitalist countries.