The U.S. army in Europe was under the command of General John J. Pershing. At first, the U.S. had few trained troops to send over to Europe. However, the army was quickly built up through the draft and volunteers. By the end of the war around 2 million U.S. troops were in France. American troops on way to the front march thru London Source: Department of Defense The U.S. troops arrived just in time to turn the tide of the war in favor of the Allies. Both sides were exhausted and running out of soldiers. The influx of fresh troops helped to boost the morale of the Allies and played a major role in the defeat of the Germans.