The Empire of Japan was the leader of the Axis powers in the Pacific Theatre . Some scholars consider the outbreak of the Second Sino-Japanese War , which began when Japan invaded China after the Marco Polo Bridge Incident in 1937 , to be the true beginning of World War II . This conflict merged with the world war following Japan 's attack on Pearl Harbor in December 1941 , which was immediately followed by a series of coordinated attacks on the U.S.-held Philippines , Guam and Wake Island ; on the British colonies of Malaya , Singapore , and Hong Kong ; and on the Kingdom of Thailand . During 1942 Japan launched offensives in the China , Southeast Asian , and Pacific Theatres of the war . By late 1942 Japan was on the defensive as the Allies reversed its earlier gains . The Atomic bombings of Hiroshima and Nagasaki by the United States , together with the declaration of war by the Soviet Union , convinced the Japanese government to surrender unconditionally on September 2 , 1945 . Many political and military leaders from Japan were convicted for war crimes before the Tokyo tribunal and other Allied tribunals in Asia
convicted for war crimes
Japanese war crimes
World War II by country