
Extract the answer to the question from the following context.
Question: The Soviet Union came about as a result of the Russian revolutionary war, but by what event was this instance already concluded?
Context: The first half of the 20th century in Russia and the Soviet Union was marked by a succession of wars, famines and other disasters, each accompanied by large-scale population losses. Stephen J. Lee estimates that, by the end of World War II in 1945, the Russian population was about 90 million fewer than it could have been otherwise.

World War II
