High Quality Content by WIKIPEDIA articles! The American Expeditionary Forces or AEF was the United States Armed Forces sent to Europe in World War I. During the United States campaigns in World War I the AEF fought in France alongside British and French allied forces in the last year of the war, against Imperial German forces. The AEF helped the French Army on the Western Front during the Aisne Offensive (at Château-Thierry and Belleau Wood) in June 1918, and fought its major actions in the Saint- Mihiel and Meuse-Argonne Offensives in late 1918.