World War II enabled its participants to employ airpower in devastating ways thatWorld War I only hinted at, particularly its use against civilians to erode their morale and support for the war. The Japanese and German air forces first demonstrated the capabilities of bomber planes with attacks against Shanghai, Warsaw, and Rotterdam in the early days of World War II, but the Allies upped the ante with sustained attacks against Germany starting in 1942 and Japan two years later. The United States sought to use a long-range bombing offensive against the Japanese home islands to cripple its wartime industry and weaken its ability to resist an amphibious invasion that U.S. forces were planning for late 1945.