Japan entered the war on the side 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. ... The Japan already had a military alliJapan's aggressive actions against China and quick economic expansion during World War I—while the great powers of Europe were occupied elsewhere—would have far-reaching effects over the course of the 20th century with Britain, but that did not obligate it to enter the war.
