Comintern
In March 1919 leading members of the Communist Party in Russia founded the Communist International (later known as Comintern). The aim of the organization was to fight "by all available means, including armed force, for the overthrow of the international bourgeoisie and for the creation of an international Soviet republic as a transition stage to the complete abolition of the State".
To be admitted to the Comintern the Communist parties had to accept twenty-one conditions. This included: (1) conduct truly Communist propaganda and agitation and uphold the ideal of a dictatorship of the proletariat before the masses; (2) remove all reformists and supporters of centrists opinions from responsible posts; (3) create an illegal (in addition to the legal) organization for subversive work.
Gregory Zinoviev, was elected chairman of the Comintern. He held the post for seven years before being dismissed by Joseph Stalin because of his support for the ideas of Leon Trotsky. Zinoviev was replaced by Nickolai Bukharin but he was dismissed in 1928 and Stalin, as General Secretary of the Communist Party, became the head of Comintern. He then purged all members of the organization who supported Trotsky and his views on world revolution.
Primary Sources
(1) Walter Krivitsky, I Was Stalin's Agent (1939)
For many years, while revolutionary prospects there seemed promising, the Comintern poured the greater part of its money into Germany and Central Europe. But when it became more decisively an appendage of the Soviet Government, and revolutionary objectives were side-tracked in favour of Stalinizing public opinion and capturing key positions in the democratic governments, Moscow's budgets for France, Great Britain and the United States were enormously increased.
(2) John Gates, The Story of an American Communist (1959)
The Cominform described the world as divided into two sharply drawn camps, the camp of imperialism and war headed by the United States, and the camp of socialism and peace, headed by the Soviet Union; all trends of neutralism toward these two camps were roundly condemned. The concept of independent roads to socialism which had flourished briefly was now denounced; the similarity of the new Communist countries and the Soviet Union was emphasized now, and all Communist countries were called on to follow the Soviet pattern in every aspect of life with disastrous consequences to their economies and liberties.
Whoever resisted these new policies was now ruthlessly purged. The Yugoslav Communists, standing up against all pressures, were expelled from the Cominform in July 1948 and excommunicated from world communism, and Tito's government denounced as pro-capitalist, even fascist. This in turn set the stage for vast new purges. Since Tito was the worst of all possible enemies, anyone associated with him or with his ideas of an independent, national development of socialism was considered an imperialist spy deserving to be eliminated. In frame-up trials (which I did not then view as frame-ups and fully endorsed), Slansky, Rajk, Kostov and others were executed, while Gomulka, Kadar and many more were removed in disgrace and thrown into prison.