In 1917, two revolutions swept through Russia, ending centuries of imperial rule and setting in motion political and social changes that would lead to the formation of the Soviet Union. In March, growing civil unrest, coupled with chronic food shortages, erupted into open revolt, forcing the abdication of Nicholas II (1868-1918), the last Russian czar. Just months later, the newly installed provisional government was itself overthrown by the more radical Bolsheviks, led by Vladimir Lenin (1870-1924).