Final answer:
General John J. Pershing became the supreme commander of the AEF in May 1917 and led the force to several key victories in World War I.
Step-by-step explanation:
Who Became Supreme Commander of the AEF in May 1917?
General John J. Pershing became the supreme commander of the American Expeditionary Force (AEF) in May 1917. Under his leadership, the AEF made significant contributions to the Allies' war effort in World War I. Pershing initially used American troops mostly as replacements for Allied casualties, but the AEF eventually fought as an independent force. Their victories in battles such as Cantigny, Chateau-Thierry, Belleau Wood, the Second Battle of Marne, Saint-Mihiel, and in the Meuse-Argonne area were instrumental in stopping German advances and aiding in the eventual armistice on November 11, 1918.
The term doughboys, often used to refer to the AEF soldiers, came from the white belts they wore, which were cleaned with pipe clay, also known as 'dough'. The AEF's successful engagements on the Western Front after the German Spring Offensive, and their contributions to the counteroffensives in August 1918, significantly exhausted Germany's military forces. This set the stage for the abdication of Kaiser Wilhelm II and the end of hostilities.