During his rule, political paranoia fermented and the Great Purge removed Stalin’s opponents within and outside of the party via arbitrary arrests and persecutions of many people, resulting in at least 600,000 deaths. In 1933, a major famine struck the country, causing the deaths of 3 to 7 million people. Before the start of World War II in 1939, the Soviets signed the Molotov–Ribbentrop Pact, agreeing to non-aggression with Nazi Germany, after which the USSR invaded Poland on 17 September 1939.
In June 1941, Germany broke the pact and invaded the Soviet Union, opening the largest and bloodiest theatre of war in history. One of the most remarkable aspects of Soviet life was the nation’s scientific ambition. The USSR invested heavily in research, particularly in physics, chemistry, medicine, and engineering. Universities and technical institutes produced highly skilled professionals who were respected across the world.
