Japan's attack on America at Pearl Harbor on December 8, 1941, changed the whole perspective of the war. China officially declared herself at war with Japan. The war against Japan now became part of the Second World War. Chiang was appointed Supreme Commander for the Allied forces in the China Theater.
民國三十年十二月八日，珍珠港事變，我國乃正式對日本宣戰，抗戰遂與世界大戰結為一體，蔣公經推選為盟軍中國戰區最高統帥。