Military Victory Depended on Alliances and Mobilization
World War II grew from expansion by Nazi Germany, Fascist Italy, and imperial Japan and weak international responses. Germany invaded Poland in 1939, while Japan had already waged major war in China. After Japan attacked Pearl Harbor on December 7, 1941, the United States declared war on Japan; Germany and Italy then declared war on the United States. American strategy operated through an alliance whose members bore different costs. United States industry produced ships, aircraft, vehicles, weapons, food, and supplies on immense scale. Farms, railroads, ports, science, taxes, bonds, and federal contracts supported operations. Allied advances from east and west defeated Nazi Germany; naval-air and island campaigns moved toward Japan. The United States dropped atomic bombs on Hiroshima and Nagasaki in August 1945, and Japan surrendered amid Soviet entry into the war. Historians debate necessity, alternatives, timing, civilian harm, and how each factor influenced surrender