Japanese entry into World War I

Japan entered World War I as a member of the Allies on 23 August 1914, seizing the opportunity of Imperial Germany's distraction with the European War to expand its sphere of influence in China and the Pacific. There was minimal fighting. Japan already had a military alliance with Britain, but that did not obligate it to enter the war. It joined the Allies in order to make territorial gains. It acquired Germany's scattered small holdings in the Pacific and on the coast of China.

The other Allies pushed back hard against Japan's efforts to dominate China through the Twenty-One Demands of 1915. Japan's occupation of Siberia against the Bolsheviks proved unproductive. Japan's wartime diplomacy and limited military action produced few results. At the Paris Peace Conference in 1919, Japan was largely frustrated in its ambitions.