With the end of conventional European imperialism, there were three groups of states, or three worlds; the industrial, developed, capitalist world; the socialist world of Eastern Europe and China; and the third world of newly liberated and underdeveloped states.
The theory, which with the abdication of communist despotisms in Eastern Europe became out of date, was more generally criticized for oversimplification; and for being applicable only to states, not to peoples or to political movements.
Aijaz Ahmad, In Theory: Classes, Nations, Literatures (London, 1992)
In the field of international relations, the Three Worlds Theory (simplified Chinese: 三个世界的理论; traditional Chinese: 三個世界的理論; pinyin: Sān gè Shìjiè de Lǐlùn) by Mao Zedong proposes three politico-economic worlds: the First world, the Second world, and the Third world. In 1974, at the United Nations, Vice-Premier Deng Xiaoping applied the Three Worlds Theory during the New International Economic Order presentations about the problems of raw materials and development, to explain the PRC’s economic co-operation with non-communist countries.
The First world comprises the US and the USSR, the superpower countries respectively engaged in imperialism and in social imperialism. The Second world comprises Japan and Canada, Europe and the countries of the global North–South divide. The Third world comprises the countries of Africa, Latin America, and continental Asia.
As political science, the Three Worlds Theory is a Maoist interpretation and geopolitical reformulation of international relations, which is different from the Three-World Model, created by the demographer Alfred Sauvy, wherein the First World comprises the US, Great Britain, and their allies; the Second World comprises the Soviet Union, the People’s Republic of China, and their allies; and the Third World comprises the economically underdeveloped countries and the countries, including the 120 countries of the Non-Aligned Movement (NAM)