After the revolution of 1905, Russia had become a constitutional monarchy. However, mounting discontent concerning food shortages and other internal problems continued to increase until it ultimately culminated in the February Revolution which saw the abdication of Tsar Nicholas II. In October, a second revolution occurred, and the provisional government was overturned by the Bolsheviks. As a result of the Russian Revolution, the Soviet Union was established and would exist until its collapse in 1991.