Stalin secured control of the Soviet Communist Party in 1923 and became Prime Minister in May 1941 until his death in 1953. He was a brutal leader, who purged his political and personal opponents. During the war he controlled the Soviet military effort as Commissar of Defence and Marshal of the Soviet Union. After signing the Nazi-Soviet non-agression pact in 1939, Soviet troops moved into Eastern Poland, the Baltic States and Finland.
The period of co-operation between Germany and the Soviet Union was short-lived however, and Russia was unprepared when the invasion by German forces began in June 1941. Britain became allied with the Soviet Union, but was unable to immediately accept Stalin’s demands for a campaign in France to relieve pressure on Russia. Stalin’s military strategy was eventually successful, but at the cost of millions of Soviet lives. At the end of the war, with the exception of Yugoslavia, the East European states ‘liberated’ by the Red Army came under the control of the Soviet Union.