American Military History, Volume 2 by Richard W. Stewart

In World War II, for the first time, the United States had to fight a war on two fronts. The central strategic principle governing al- location of resources to the two fronts provided for concentrating first on the defeat of the European Axis. The Americans liberally inter- preted this principle, permitting an offensive war against Japan as well as against Germany in the years 1943–1945. The U.S. Fleet, expand- ing after its initial setback at Pearl Harbor, provided the main sinews for an offensive strategy in the Pacific. The Army devoted at least one- third of its resources to the Pacific war even at the height of war in Europe. In short, the United States proved capable, once its resources were fully mobilized, of successfully waging offensives on two fronts simultaneously, a development the Japanese had not anticipated when they launched their attack on Pearl Harbor.