Nanyo (南洋 Nan'yō, literally South Seas) was the Japanese League of Nations mandate consisting of several groups of islands (modern-day Palau, Northern Mariana Islands, Federated States of Micronesia, and Marshall Islands) in the Pacific Ocean which came under the administration of Japan after the defeat of the German Empire in World War I.
The administration of Nanyo was originally the responsibility of the Imperial Japanese Navy, which divided the territory into six administrative districts reporting to the naval headquarters in Truk. Later, in April 1922, a civilian government was established in each of the six administrative districts (Saipan, Palau, Yap, Truk, Ponape and Jaluit Atoll) in the form of a civil administration department which still reported to the local naval garrison commander.
Later, the headquarters of the Nanyo government was moved from Truk to Koror, Palau; and the Governor of Nanyo began to report directly to the Prime Minister of Japan. After the establishment of the Ministry of Colonial Affairs in June 1929, the Governor reported to the Minister of Colonial Affairs instead.
When the Ministry of Colonial Affairs was absorbed into the Ministry of Greater East Asia in November 1942, the primacy of the Imperial Japanese Navy was again recognized by the appointment of an admiral as the Governor. Furthermore, the six administrative districts were reduced to three in November 1943: North, East, and West.