After the defeat of the Reds in the Finnish Civil War, he fled to the Soviet Union, where he worked until his death.

He briefly led the Finnish Democratic Republic before serving as Chairman of the Presidium of the Supreme Soviet of the Karelo-Finnish SSR.

He was a leader of the January 1918 revolution in Finland that created the short-lived Finnish Socialist Workers' Republic, of which he was appointed People's Commissar of Education.

Kuusinen continued his work as a prominent leader of the Comintern in Bolshevist Russia, that soon became the Soviet Union.

Animosity towards socialists in Finland in the decades after the civil war prompted many Finns to emigrate to Russia to "build socialism."

Many Finnish communists sympathetic to Trotskyism or social democracy were purged and Kuusinen's reputation in Finland was damaged when he turned out to be one of the very few not targeted by Stalinist show trials, deportations, and executions.

When the Red Army began its advance during the Winter War on November 30, 1939, Kuusinen was pronounced head of the Finnish Democratic Republic (also known as the Terijoki Government)—Joseph Stalin's puppet regime[3][4][5][6] through which Finland would be transformed into a socialist state.

According to him, Kuusinen would have known that the underground Finnish Communist Party was in shambles due to police terror and could not incite a mass revolt in Finland or mutiny in the ranks of the army.

[7] The Finnish Communist Party had little influence during the 1930s and most working class Finns stood behind the legal government in Helsinki.

After learning that he was terminally ill, Kuusinen requested (via the Helsinki Embassy of the Soviet Union) permission to visit Laukaa and Jyväskylä as a private person.

[10][11]The quote "solar system of organizations" was wrongly ascribed to Lenin by U.S. HUAC chief investigator Robert E. Stripling[12] and U.S. Attorney General Francis Biddle.