World War II transformed Japan from an imperial power to an occupied nation. The conflict began with Japan's invasion of China in 1937 and ended with its surrender in 1945 after the atomic bombings of Hiroshima and Nagasaki. The U.S.-led Allied Occupation from 1945 to 1952 reshaped Japan's political, economic, and social structures. Key reforms included demilitarization, land redistribution, and the adoption of a new constitution, setting the stage for Japan's postwar recovery and development.