The Empire of Japan invaded other parts of China in 1937 , precipitating the Second Sino-Japanese War ( 1937 – 1945 ) . The Imperial Japanese Army swiftly captured the capital Nanjing and conducted the Nanjing Massacre . In 1940 , the Empire invaded French Indochina , after which the United States placed an oil embargo on Japan . On December 7 – 8 , 1941 , Japanese forces carried out surprise attacks on Pearl Harbor , British forces in Malaya , Singapore and Hong Kong and declared war on the United States and the British Empire , bringing the United States and the United Kingdom into World War II in the Pacific . After Allied victories across the Pacific during the next four years , which culminated in the Soviet invasion of Manchuria and the atomic bombings of Hiroshima and Nagasaki in 1945 , Japan agreed to an unconditional surrender on August 15 . The war cost Japan , its colonies , China and the war 's other combatants tens of millions of lives and left much of Japan 's industry and infrastructure destroyed . The Allies ( led by the United States ) repatriated millions of ethnic Japanese from colonies and military camps throughout Asia , largely eliminating the Japanese empire and restoring the independence of its conquered territories . The Allies also convened the International Military Tribunal for the Far East on May 3 , 1946 , to prosecute some senior generals for war crimes
war crimes
Japanese war crimes
Japan