Final answer:
The Russian Civil War occurred from 1918 to 1921, leading to the establishment of the Soviet Union with high casualties.
Step-by-step explanation:
The Russian Civil War, which pitted the Red Army against the White Army, took place during the years 1918-1921. This bloody conflict followed the Bolshevik takeover in 1917, leading to the eventual victory of the Bolsheviks and the formation of the Soviet Union.
Numerous countries, including Britain, France, Japan, and the United States, intervened in support of the White Army but were unsuccessful in preventing the Bolsheviks from seizing control. The war resulted in a high casualty count, with approximately 1.5 million soldiers and an estimated civilian death toll of about eight million, predominantly from massacres and starvation.