Throughout most of its existence and history, the Fourth International was hunted by agents of the NKVD, subjected to political repression by countries such as France and the United States, and by supporters of the Soviet Union.

The Fourth International struggled to maintain contact under these conditions of crackdowns and repression during World War II due to the fact that subsequent proletarian uprisings were often under the influence of Soviet-aligned pro-Stalin parties and militant nationalist groups, leading to defeats for the Fourth International and the Trotskyists, who subsequently never managed to obtain meaningful influence.

[2] Despite this, many parts of the world, including Latin America, Europe and Asia, continue to have large Trotskyist groupings who are attracted to its anti-Stalinist positions and its defense of proletarian internationalism.

A partial reunification of the schismatic factions occurred in 1963, but the organization never recovered sufficiently, and it failed to re-emerge as a single transnational grouping.

[1] In the Transitional Program, which was drafted during the founding congress of the Fourth International, Trotsky called for the legalization of the Soviet parties and worker's control of production.

[12] By declaring themselves the Fourth International, the "World Party of Socialist Revolution", the Trotskyists were publicly asserting their continuity with the Comintern, and with its predecessors.

[5] The foundation of the Fourth International was therefore spurred in part by a desire to form a stronger political current, rather than being seen as the communist opposition to the Comintern and the Soviet Union.

[25] The Transitional Programme was the central programmatic statement of the congress, summarising its strategic and tactical conceptions for the revolutionary period that it saw opening up as a result of the war which Trotsky had been predicting for some years.

It is not, however, the definitive programme of the Fourth International – as is often suggested – but instead contains a summation of the conjunctural understanding of the movement at that date and a series of transitional policies designed to develop the struggle for workers' power.

The resident International Executive Committee failed to meet, largely because of a struggle in the U.S. Socialist Workers Party (SWP) between Trotsky's supporters and the tendency of Max Shachtman, Martin Abern and James Burnham.

[30] Trotsky opened a public debate with Shachtman and Burnham and developed his positions in a series of polemics written in 1939–1940 and later collected in In Defense of Marxism.

It adopted a manifesto drafted by Trotsky shortly before his murder and a range of policies on the work of the International, including one calling for the reunification of the then-divided Fourth Internationalist groups in Britain.

[34] Despite this dislocation, the various groups sought to maintain links and some connections were kept up throughout the early part of the war by sailors enlisted in the U.S. Navy who had cause to visit Marseille.

[36] In 1942, a debate on the national question in Europe opened up between the majority of the SWP and a movement led by Van Heijenoort, Albert Goldman and Felix Morrow.

[citation needed] The wartime debate about post-war perspectives was accelerated by the resolution of the February 1944 European Conference of the Fourth International.

The European conference extended the lessons of a revolution then unfolding in Italy, and concluded that a revolutionary wave would cross Europe as the war ended.

[41] The British Revolutionary Communist Party (RCP) disagreed and held that capitalism was not about to plunge into massive crisis but rather that an upturn in the economy was already underway.

In France, they backed elements, including Pierre Frank and Marcel Bleibtreu, opposed to the new leadership of the PCI – albeit for differing reasons.

This was initially denied by Mandel (who was quickly forced to revise his opinion, and later devoted his PhD dissertation to late capitalism, analysing the unexpected "third age" of capitalist development).

Mandel's perspective mirrored uncertainty at that time about the future viability and prospects of capitalism, not just among all Trotskyist groups, but also among leading economists.

Paul Samuelson had envisaged in 1943 the probability of a "nightmarish combination of the worst features of inflation and deflation", worrying that "there would be ushered in the greatest period of unemployment and industrial dislocation which any economy has ever faced".

[53] In their analysis, it differed from the rest of the Eastern Bloc because it was established by the partisans of World War II who had fought against Nazi occupation, as opposed to by Stalin's invading armies.

[56] In line with this geopolitical perspective, Pablo argued that the only way the Trotskyists could avoid isolation was for various sections of the Fourth International to undertake long-term entryism in the mass Communist or Social Democratic parties.

The French section disagreed with the associated tactic of entryism sui generis, and held that Pablo was underestimating the independent role of the working class parties in the Fourth International.

The leaders of the majority of the Trotskyist organisation in France, Marcel Bleibtreu and Pierre Lambert, refused to follow the line of the International.

[63] An excerpt from the Open Letter explains the split as follows: To sum up: The lines of cleavage between Pablo's revisionism and orthodox Trotskyism are so deep that no compromise is possible either politically or organizationally.

[69] According to Robert Alexander, Ernest Mandel has written that an organisation in Indonesia, the Partai Acoma, was affiliate to the FI from 1959 until the 1965 coup in that country.

[70] The Sixth World Congress in 1961 marked a lessening of the political divisions between the majority of supporters of the International Secretariat and the leadership of the SWP in the United States.

[citation needed] Echoing Marx's Communist Manifesto, the Transitional Programme ended with the declaration "Workers – men and women – of all countries, place yourselves under the banner of the Fourth International.

[citation needed] Those groups which follow traditions that left the Fourth International in its early years argue that, despite initially correct positions, it had little impact.