Altiero Spinelli in the context of "Founding fathers of the European Union"

Eurocommunism was a trend in the 1970s and 1980s within various Western European communist parties, which said they had developed a theory and practice of social transformation more relevant for Western Europe. During the Cold War, they sought to reject the influence of the Soviet Union and its Communist Party. The trend was especially prominent in Italy, Spain, and France. It is commonly considered to have been prompted by the Prague Spring. Although the various parties converged against the Soviet factor, their own doctrines remained as different at the dissolution of the movement as they originally were before 1968.

The Union of European Federalists (UEF) is an international non-profit association originally founded in 1946 and refounded in 1973, promoting the advent of a European federal state based on the idea of unity in diversity.In 1946, it brought together a number of initiatives, particularly from the Resistance, aimed at creating a European federation, including the Movimento Federalista Europeo created the day after the fall of Benito Mussolini in Milan from 27 to 29 August 1943, under the impetus of the opponent Altiero Spinelli, among others, and the French Committee for the European Federation created in Lyon by members of the "Francs-tireurs" group in June 1944.

The European Federalist Movement (Movimento Federalista Europeo, MFE) was founded in Milan in 1943 by a group of activists led by Altiero Spinelli. The principles which inspired its foundation are contained in the Ventotene Manifesto, drawn up in 1941 by Spinelli himself,Eugenio Colorni, Ursula Hirschmann and Ernesto Rossi, and circulated by the in May 1943 circulated L'Unità europea periodical. Vayssière notes that the manifesto is widely seen as the birth of European federalism. Spinelli (1907–86), a former Communist, became a leader of the federalist movement due to his primary authorship of the Manifesto and his postwar advocacy. The manifesto called for a break with Europe's past to form a new political system through a restructuring of politics and extensive social reform. It was presented not as an ideal, but as the best option for the Europe's postwar condition.

Federalism represented in the 1940s a revolutionary and entirely innovative political idea. According to the federalists, the new line between progressive and reactionary forces was the one that existed between those for whom the key task is to create a federal European state, and those who consciously or de facto acted to maintain a diversity of sovereign nation-states.