The 20th Party Congress was an important annual meeting of the Soviet Union's Communist party delegates that occurred in February 1956.
Like all Party Congresses, this one was supposed to be secret. Nikita Khrushchev, the Communist Party Secretary, took this opportunity to give a stinging rebuke of the policies of his late predecessor, Joseph Stalin. Khrushchev denounced Stalin's cult of personality, and Stalin's apparent support of the concept of individuality. He went on to denounce a list of crimes committed by Stalin's supporters, many of which had previously been denied by the Soviet Union.
The speech was not intended for anyone other than the Communist delegates, as it was essentially a quiet reversal of years of Soviet propaganda, namely that Stalin was a wise, peaceful, and fair leader. However, an Israeli Mossad agent was secretly in attendance of the meeting, and obtained a copy of Khrushchev's speech. Within days the speech was circulated all over the western media, causing a massive embarrassment to the Soviet Union, and many conflicts in global communist movements.
One of its most notable fallouts was the collapse of the United States Communist Party which had previously been composed of many die-hard Stalinists. Stalin's fall from grace left the party badly fractioned, and it never regained its former influence.