How did the arrival of the aef affect the allies' war effort?

During World War I, the arrival of the American Expeditionary Force (or, AEF) affected the Allied war effort in numerous ways, including on the front line of the Western Front itself. And yet, it was the energy and optimism of the indomitable American spirit that may have been most significant, as these provided the war-weary Europeans with a significant morale boost at a critical time.