The military history of the United States in World War II covers the war against Germany, Italy, Japan, starting with the 7 December 1941 attack on Pearl Harbor. During the first two years of World War II, the United States had maintained formal neutrality while supplying Britain, the Soviet Union, and China with war material through the Lend-Lease Act which was signed into law on 11 March 1941, as well as deploying the U.S. military to replace the British invasion forces in Iceland.
U.S economic sanctions on Japan as part of the effort to deter Japanese military aggression in Asia and the Pacific outraged the Empire of Japan as the major cause of Japanese attack on Pearl Harbor. During the war, over 16 million Americans served in the United States Armed Forces, with 290,000 killed in action and 670,000 wounded.
Admiral Chester W. Nimitz was responsible for planning a series of some of the most famous naval battles in history. Japan’s main carriers were sunk during the Battle of Midway, and the Americans seized the initiative against the entrenched Japanese forces. The Pacific War became one of island hopping, moving air bases closer and closer to Japan. With its merchant fleet sunk, Japan ran short of aviation gasoline and fuel oil, as the U.S. Navy in June 1944 captured islands within bombing range of the Japanese home islands. Strategic bombing destroyed all the major Japanese cities, as the U.S. captured Okinawa after heavy losses in spring 1945. With the atomic bombings of Hiroshima and Nagasaki and an invasion and Soviet intervention imminent, Japan surrendered.
The war against Germany began with aid to Britain, her allies, and the Soviet Union, with the U.S. supplying munitions until it could ready an invasion force. The main invasion of France took place on June 6, 1944. Meanwhile, the U.S. Army Air Forces and the British Royal Air Force engaged in the area bombardment of German cities, systematically targeting German transportation links and synthetic oil plants, as it destroyed what was left of the Luftwaffe. With the Soviets unstoppable in the east, and the Allies unstoppable in the west, Germany was squeezed to death. Berlin fell to the Soviets in May 1945, and with Adolf Hitler dead, the Germans surrendered.