 Molotov was the principal Soviet signatory of the Nazi – Soviet non @-@ aggression pact of 1939 ( also known as the Molotov – Ribbentrop Pact ) , whose most important provisions were added in the form of a secret protocol that stipulated an invasion of Poland and partition of its territory between Germany and the Soviet Union . This effectively marked the beginning of World War II and made the Soviet Union an unofficial ally of Nazi Germany in the period from 1939 until the German invasion in 1941 . During this period , Molotov knew of the Katyn massacre committed by the Soviet authorities . Following the end of World War II ( Great Patriotic War ) , Molotov was involved in negotiations with the Western allies , in which he became noted for his diplomatic skills . He kept his place as a leading Soviet diplomat and politician until 1949 . In March of that year , after losing Stalin 's favour , he lost the foreign affairs ministry leadership to Andrei Vyshinsky . Molotov 's relationship with Stalin deteriorated further , with Stalin complaining about Molotov 's mistakes in a speech to the 19th Party Congress . However , after Stalin 's death in 1953 , Molotov was staunchly opposed to Khrushchev 's de @-@ Stalinisation policy . Molotov defended the policies and legacy of Stalin until his death in 1986 , and harshly criticised Stalin 's successors , especially Khrushchev . 
