The German scientist Fritz Haber was a paradoxical figure. During World War I, he gained notoriety as the inventor of mustard gas, which added a new dimension of suffering to the western front. Haber’s culpability apparently drove his pacifist wife, who was also a scientist, to commit suicide in 1915; perhaps she would have been prouder of Haber’s Nobel Prize, which he won in 1918 for synthesizing ammonia, a vital tool in the development of fertilizers. Haber’s is one of the stories that Preston tells about the spring of 1915, when imperial Germany, frustrated by the war’s stalemate, sought to break its enemies’ wills by employing new forms of warfare: first poison gas, then submarine attacks, and finally zeppelin raids. Preston opens this vivid, compelling book by discussing the Hague Conventions of 1899 and 1907, which sought to humanize the conduct of war by establishing codes of conduct that would spare noncombatants. Crudely disregarding those rules did not help Germany turn the tide of the war: in fact, it made matters worse for the Germans, by drawing the United States into the fight.