Dependency theory is an international political and economic theory emerging in 1960s. It was intended to apply the dependency between core countries and peripheral countries to explain the underdevelopment in peripheral countries, and it attributed such an underdevelopment to external reasons. According to the dependency theory, the motion law and economic conflicts of capitalism forced this system to extend to underdeveloped periphery in the world economy; due to the insufficient consumption and reduced profitability in the home country, capitalist countries would certainly control and exploit underdeveloped countries, which led to the hierachical ruling structure between the industrial center and the dependent periphery. There’s no systematic theoretical structure for dependency theory.

The world system theory is a widely influential theory emerging during 1970s. It attempted to analyze the historical evolution of the world system with variables like dependency between the core and the periphery, the world labor division and class conflicts, then explain the world development history since the 16th century. According to this theory, the world system bears a unitary world economic foundation; labor division divided the world into three zones: the central zone, the semi-peripheral zone and the peripheral zone; the global expansion of capitalism gradually integrated the peripheral zone into the world economic system and made it marginalized; national economic positions keep changing, and the geographical distribution of national economic positions is also altering.

The study of international relations is not only a branch of politics, but also a relatively independent interdisciplinary subject, concerning politics, economics, history, sociology, and many others. The main body of international relations theory is the international political theory based on national powers. The major schools during the evolution of international politics include: 1) Realism, Neo-Realism and Neo-classical Realism; 2)Rationalism, classical liberalism, idealism, and neo-liberal institutionalism; 3}Marxism, imperialism, dependency theory, world system theory and neo-radicalism; 4) Scientific actionism; 5)Critical theory and constructivism; 6)Influence of geographical environment. Since 1970s, some new ideas emerged in the study of international relations, like post-actionism, post-structuralism, post-modernism, neo-functionalism, environmentalism, mutual dependence, new security theory, soft power theory, civilization conflict theory, democratic peace theory, neo-empire theory and the theory of hegemonic stability.