The chapter examines the background to Japanese aggression in the 1930s and the early stages of Japan’s imperialism in East Asia. The war with Nationalist China from 1937 and the resistance to Japanese aggression are put in the context of China’s recent past. The war led to the wider clash with the European empires and the United States, which ended with complete Japanese defeat in 1945. The dropping of the two atomic bombs it is argued here was a wartime atrocity but it contributed to forcing Japan’s surrender.