Mikhail Gorbachev, officially acknowledged on April 13, 1990 that the Soviet Union was responsible for the Katyn massacre in Poland in 1940, and released archival evidence confirming the crime, where nearly220,000 Polish military officers, policemen, and intelligentsia were secretly killed and buried during their occupation of eastern Poland.
The Katyn massacre was a series of mass executions of Poles carried out by the Soviet Union between April and May 1940. and followed up with a long-term cover-up. The Western Allies chose not to confront it publicly, effectively contributing to a suppression of the truth for strategic wartime reasons.
When Nazi Germany discovered the mass graves in 1943 and announced them to the world, they blamed the Soviet Union. The Soviets denied responsibility and accused the Nazis instead. Leaders like Franklin D. Roosevelt and Winston Churchill were informed through intelligence and diplomatic channels, that the Soviets were likely responsible. Publicly, the Allies accepted the Soviets' denial and blamed Nazi Germany, to preserve the wartime alliance, which was considered essential to defeating Nazi Germany
After the war, investigations, including U.S. congressional inquiry in the early 1950s; concluded that the Soviets were responsible and noted that earlier information had been intentionally suppressed for political reasons. More
