Joseph Stalin was the General Secretary of the Communist Party of the Soviet Union in the 1930s. He orchestrated the Soviet Union's Great Purge from 1936 to 1938 as a way to silence political opposition, thereby allowing him to seize absolute power in the USSR.
In addition, trade policies enforced by Stalin's government were responsible for the Holodomor of 1932–1933, during which millions of Ukranian citizens were starved to death. The Holodomor was a part of a Soviet famine of the same time period.
The USSR under Stalin was a signitory of the Molotov-Ribbentrop Pact with Nazi Germany in 1939. The pact was officially a non-agression pact between the two countries, but it also secretly divided eastern Europe into German and Soviet spheres of influence.