World War I essentially began Aug. 4, 1914, with the German army’s invasion of Belgium. The United States entered the conflict on the side of the Allies (Great Britain, Belgium, France, Italy and Russia) on April 6, 1917. During the intervening 32 months, America remained neutral – but many Americans did not. Thousands volunteered for the Allied cause. What we know of these early volunteers is based on their memoirs, if they wrote of their experiences, or from accounts of journalists.