 During World War I, many of the Germany possessions in the Pacific were conquered by Japan, who fought on the side of the Allies of World War I and was active in the Asian and Pacific theatre of World War I.The Empire of Japan administrated the islands from 1920 under the South Seas Mandate granted by the League of Nations.During this period, the Japanese population grew to over 100,000 throughout Micronesia, while the indigenous population was about 40,000.