At the outbreak of the war, the United States pursued a policy of non-intervention, avoiding conflict while trying to broker peace. After a German U-boat sank the British liner Lusitania on 7 May 1915 with 120 Americans among the dead, President Woodrow Wilson insisted that “America is too proud to fight” but demanded an end to attacks on passenger ships, and Germany complied. Wilson unsuccessfully tried to mediate a settlement, while repeatedly warning that the U.S.A. would not tolerate unrestricted submarine warfare in violation of international law, and former president Theodore Roosevelt denounced German acts as “piracy.” Wilson was narrowly reelected in 1916 as his supporters emphasized “he kept us out of war.” In January 1917, Germany resumed unrestricted submarine warfare, realizing it would mean American entry, and the German Foreign Minister, in the Zimmerman Telegram, invited Mexico to join the war as Germany’s ally against United States, promising financial support and help recovering Texas, New Mexico, and Arizona. Wilson released the Zimmerman note to the public, and Americans saw it as “a cause for war.” After the sinking of seven U.S merchant ships by submarines and the publication of the Zimmerman telegram, Wilson called for war on Germany, and the U.S. Congress declared war on 6 April 1917. The United States was never formally a member of the Allies but became a self-styled “Associated Power” and was sending 10,000 fresh soldiers to France every day. In 1917, the U.S. Congress gave U.S citizenship to Puerto Ricans when they were drafted to participate in World War I as part of the Jones Act. Germany had miscalculated, believing it would be many more months before American soldiers would arrive and that their arrival could be stopped by U-boats. The United States Navy sent a battleship group to Scapa Flow to join the British Grand Fleet, destroyers to Queenstown, Ireland, and submarines to help guard convoys, and several regiments of U.S. Marines were also dispatched to France. The British and French wanted U.S. units used to reinforce troops already on the battle lines and not use scarce shipping on bringing over supplies; the U.S. rejected the first proposition and accepted the second. General John J. Pershing, commander of the American Expeditionary Forces, refused to break up U.S. units to be used as reinforcements for British Empire and French units, though he did allow African-American combat regiments to serve in French divisions. The Harlem Hellfighters fought as part of the French 16th Division and earned a unit Croix de Guerre for their actions at Chateau-Thierry. Doctrine called for the use of frontal assaults, which British Empire and French commanders had long since discarded because of the large loss of life.