In 1917 the U.S. entered the First World War on the side of the French, the British and others against the Germans. Another major power fighting the Germans had been the Russians. But then came the Russian Revolution of October 1917, and Russia effectively dropped out of the war. So how was it that American troops were sent to Siberia to fight the Russians in 1918?
To answer that question, we need to take a look at some Russian history. When World War I broke out in 1914, the first country that Germany officially declared war on was Russia, on August 1. Declaration of war with France came on August 3, and to complete the picture, the British declared war on Germany on August 4.