The three worlds as they were separated during the Cold War era, each with its respective allies as of the period between 30 April 1975 (the fall of Saigon) and 23 August 1975 (the communist takeover in Laos). Colors do not represent current economic development.
First World: United States, United Kingdom and their allies.
Second World: Soviet Union, China, and their allies.
The Second World refers to the former Socialist, industrial states (formally the Eastern Bloc), mostly the territory and the influence of the Soviet Union. Following World War II, there were nineteen communist states, and after the fall of the Soviet Union, only five socialist states remained: China, Cuba, Laos, North Korea and Vietnam. Along with "First World" and "Third World", the term was used to divide the states of Earth into three broad categories. In other words, the concept of "Second World" was a construct of the Cold War and the term has largely fallen out of use since the revolutions of 1989, though it is still used to describe countries that are in between poverty and prosperity, many of which are now capitalist states. Subsequently, the actual meaning of the terms "First World", "Second World" and "Third World" changed from being based on political ideology to an economic definition. The three world theory has been criticized as crude and relativity outdated for its nominal ordering (1, 2, 3) and sociologists have coined the term "developed", "developing", and "underdeveloped" as replacement terms for global stratification—nevertheless, the three world theory is still popular in contemporary literature and media. This might also cause semantic variation of the term between describing a region's political entities and its people.