Answer:
D. The Russian Revolution
Step-by-step explanation:
The Soviet Union, whose official name was the Union of Soviet Socialist Republics, was founded in 1922 following the victory of the Bolsheviks in the Russian Revolution. The Revolution itself occurred in 1917 and resulted in the end of the period of the Russian Tsars. The Soviet Union played an important role in both World War II and the Cold War. After this latter conflict the USSR was dissolved and the former republics associated with it became independent nations.