The PSUM was founded in November 1981 by the merger of four
socialist parties: • The
Mexican Communist Party (, PCM) - the Mexican affiliate of the
Communist International, formed in 1919; • The
Movement of Socialist Action and Unity (, MAUS) - a split from the PCM that was active in the Mexican
Labour movement; • The
Party of the Mexican People (, PPM) - a split from the
Popular Socialist Party (PPS); • The
Movement of Popular Action (, MAP) - a party involved in campaigns for
trade-union democracy and reform in the 1970s. Before merging to form the PSUM, these four parties had formed an
electoral alliance called the
Coalition of the Left () in 1977. Though the PSUM was a multi-tendency organization, it generally followed the ideology of
Eurocommunism. In 1988, the PSUM changed its name to the Mexican Socialist Party (, PMS) after the merging with
Mexican Workers' Party. In 1989, following the presidential campaign of
Cuauhtémoc Cárdenas, the PMS joined Cárdenas and other dissidents from the
Institutional Revolutionary Party to form the
Party of the Democratic Revolution (PRD). ==References==