Comintern
Moscow's world revolutionary headquarters from 1919 to 1943, which built communist parties on every continent and subordinated all of them to Soviet foreign policy.
The Communist International, founded in Moscow in March 1919, was an organization for making revolutions in other countries. That is not a hostile characterization; it is the stated purpose. For twenty-four years the Comintern trained, funded, and directed communist parties from Berlin to Shanghai to Havana, and the single most important thing to understand about it is that those parties took orders. When Soviet foreign policy changed, the line changed everywhere within weeks, and local communists who disagreed were expelled or worse.
Twenty-one conditions
Lenin created it in the conviction that the Russian revolution would not survive alone and that Europe was about to follow. When that failed to happen, the Comintern's purpose shifted from coordinating an imminent world revolution to building disciplined parties that could make one later.
The instrument was the Twenty-One Conditions, adopted at the Second Congress in 1920. Any party wanting to join had to accept them: expel reformists and pacifists, build an illegal underground apparatus alongside the legal party, subordinate its parliamentary representatives to the party leadership, call itself Communist, and treat the decisions of the Comintern's executive as binding. The conditions were designed to split the socialist movement, and they did. In country after country, socialist parties broke into a social democratic wing and a communist wing, and the hostility between those two wings shaped European politics for the rest of the century.
The apparatus that resulted was real. The Comintern ran training schools in Moscow for foreign cadres, moved money and couriers through front organizations, and maintained an intelligence arm. Ho Chi Minh worked for it. So did Josip Broz Tito. So did the agents who built the Chinese Communist Party, which was founded in 1921 with Comintern assistance and advice.
The line changes
The cost of that discipline was that the parties had to follow Soviet interests, including when those interests were disastrous locally.
In China, the Comintern ordered the young Communist Party into an alliance with Chiang Kai-shek's Nationalists, then held to the alliance until Chiang massacred the communists in Shanghai in 1927. The survivors concluded that Moscow's advice could get them killed, which is a large part of why Mao's rural strategy eventually displaced the Comintern-approved urban line, and why the Chinese party developed an independence that later made the Sino-Soviet split possible.
In Germany, the Third Period line from 1928 instructed communists to treat social democrats as the main enemy, calling them social fascists, and forbade cooperation against the Nazis. The two largest parties of the German left spent the years of Hitler's rise attacking each other. That decision is one of the most consequential tactical errors of the twentieth century.
The reversal came in 1935, when the Seventh Congress adopted the Popular Front, instructing communists to ally with anyone against fascism. The result was the Popular Front governments in France and Spain, and Comintern organization of the International Brigades in the Spanish Civil War. Then, in August 1939, the Nazi-Soviet pact required another reversal, and communists worldwide were told to stop calling the coming war antifascist. Many left the movement then. In June 1941 they were told to reverse again.
Dissolution and afterlife
Stalin dissolved the Comintern in May 1943 as a gesture to his wartime allies, signaling that the Soviet Union was a normal state rather than the headquarters of world revolution. Nobody serious believed it. The functions moved into the Soviet Communist Party's international department, and the Cominform revived a slimmer version for Europe in 1947.
What the Comintern left behind is the template. It is the origin of the twentieth-century idea that a great power can build, fund, and steer political movements inside other countries as an instrument of statecraft, and it worked well enough that everyone eventually copied the form: American labor and cultural programs in the Cold War, Saudi religious funding, and the modern Russian and Chinese cultivation of foreign parties and influence networks. The Comintern's own record also shows the flaw in the model. A movement that must follow a foreign capital's line will sooner or later be ordered to do something suicidal at home, and the ones that survive are the ones that learn to disobey.