Just days before the outbreak of World War II, the world was shocked by the announcement of a non-aggression pact between two sworn enemies: Nazi Germany and the Soviet Union. Formally known as the Molotov-Ribbentrop Pact, it guaranteed that neither power would attack the other. However, the agreement contained a secret protocol that divided Eastern Europe into 'spheres of influence.' They effectively planned the joint invasion and partition of Poland, while giving the USSR a free hand in the Baltic States and Finland. For Hitler, this secured his eastern flank, allowing him to invade Poland without fear of Soviet intervention. For Stalin, it bought time to modernize the Red Army. The pact remained in effect until Hitler betrayed Stalin by launching Operation Barbarossa in 1941.