when did the us begin sending large numbers of troops to join world war i in europe
History of the United States Army The United States joined World War I in April 1917 on the side of the Triple Entente (British Empire, France, and Russia). Because of the necessary period of training before the units were moved overseas, the first elements of the American Expeditionary Forces arrived in June 1917. Their first actions of the Western Front came in October 1917. U.S. troops contributed to the offensive that finally broke through the German lines. With the armistice on 11 November 1918, the Army once again decreased its forces.