Answer
Joffre helped organize the armies of the United States during WWI. The United States entered the war in 1917, and Joffre was sent to the United States to help organize and train the American Expeditionary Forces (AEF). Joffre's experience and expertise were invaluable to the AEF, and he helped to ensure that the United States was able to make a significant contribution to the Allied victory in the war.