Kwantung Leased Territory
By the outbreak of World War I the empire included Taiwan, Korea, the Ryukyu Islands, the southern half of Sakhalin island (Karafuto Prefecture), the Kuril Islands, and Port Arthur (Kwantung Leased Territory). The policy of "Nanshin-ron" ("Southern Expansion Doctrine"), popular with the Imperial Japanese Navy, held that Southeast Asia and the Pacific Islands were the area of greatest potential value to the Japanese Empire for economic and territorial expansion.