Seized from Germany by the Japanese during World War I. Japan ruled through a League of Nations Mandate beginning in 1920 until it left the League of Nations in 1935. Major islands are Palau, Yap and Truk. Palau is 190 square miles, Yap around 40 square miles. In the 1930s, Palau was the administrative center for Japan's holdings in Micronesia and had a Japanese civilian population of around 26,000. The Japanese built a military base on Yap in the 1930s, and Truk became Japan's fleet anchorage for the Central Pacific.