The Fourth International Posadist is a Trotskyist international. It was founded in 1962 by J. Posadas, who had been the leader of the Latin America Bureau of the Fourth International in the 1950s, and of the Fourth International's section in Argentina.
As an ideology Posadism supports the potential for Third World revolution, is enthusiastic about nuclear war and space exploration by the former USSR and the People's Republic of China, and has an esoteric concern for "harmonisation" and "man's relationship to the earth, to nature and to the cosmos", based upon an original analysis of working class culture developed by J. Posadas.
Some detractors have made allegations that the Posadists believe in a New Age doctrine based upon a millenarian belief in UFOs coming from a socialist future or alien socialist planet, and that fringe science experiments involving dolphins and water birth are also popular themes among Posadas' followers. The Colombian section of the Posadist International denies this as an "attempt by the Colombian media to smear us".
When the FI split in 1953 Posadas and his followers sided with Michel Pablo and the International Secretariat of the Fourth International. The Posadists began quarrelling with the majority of the ISFI in 1959 over the question of nuclear war with Posadas being a proponent as, he claimed, it would destroy capitalism and clear the way for socialism. The Posadists finally split with the ISFI in 1962 to form the Fourth International (Posadist). The group initially had a following in several countries, particularly among railway workers in Cuba, tin workers in Bolivia and farm workers in Brazil. At its peak in the late 1960s the Posadists had approximately 1,000 members worldwide.