During the period of US neutrality from 1914-1917, thousands of American men and women volunteered to serve in the war zone as doctors, nurses, ambulance drivers, soldiers, or fighter pilots. Axel Jansen uses letters, diaries, and other material from archives in the US and Europe to investigate their motives, and to explain why these American citizens did not call for US intervention in the "European War" even though they chose to go abroad to aid the Allies.