[14] During the post-World War II period, the SI aided social democratic parties in re-establishing themselves when dictatorship gave way to democracy in Portugal (1974) and Spain (1975).

In the late 1970s and in the 1980s the SI had extensive contacts and discussion with the two leading powers of the Cold War period, the United States and the Soviet Union, on issues concerning East–West relations and arms control.

[16] Since then, the SI has admitted as members an increasing number of parties and organisations from Africa, Asia, Europe, and Latin America (see below for current list).

For a long time, the Socialist International remained distant from Latin America, considering the region as a zone of influence of the United States.

For example, it did not denounce the coup d'état against Socialist President Jacobo Árbenz in Guatemala in 1954 or the invasion of the Dominican Republic by the United States in 1965.

It was not until the 1973 Chilean coup d'état that "a world we did not know" was discovered, explained Antoine Blanca, a diplomat for the French Socialist Party.

According to him, solidarity with the Chilean left was "the first challenge worthy of the name, against Washington, of an International which, until then, had done everything to appear subject to American strategy and NATO".

Subsequently, notably under the leadership of François Mitterrand, the SI supported the Sandinistas in Nicaragua and other movements in El Salvador, Guatemala, and Honduras in their struggle against US-supported dictatorships.

In the following decade, many left-wing parties that came to power (in Brazil, Venezuela, Bolivia, Ecuador and El Salvador) preferred to keep their distance from the SI.