After the First World War, the League of Nations granted Japan a mandate over the CarolineMarshall, and Mariana Islands in the central Pacific.  These former German territories, known to the Japanese as the Nan'yō guntō ("South Seas islands"), were to be governed for the betterment of their inhabitants. To the Japanese, this meant inculcating the natives with Japanese culture and making them loyal subjects of the Emperor. The United States failed to join the League of Nations, but signed a convention with Japan in February 1922 that recognized the League mandate.

Japan held these territories under a Class C mandate, as defined in Article 22.6 of the Covenant of the League of Nations:

There are territories, such as South West Africa and certain of the South Pacific Islands, which, owing to the sparseness of their population, or their small size, or their remoteness from the centres of civilisation, or their geographical contiguity to the territory of the Mandatory, and other circumstances, can be best administered under the laws of the Mandatory as integral portions of its territory, subject to the safeguards above mentioned in the interests of the indigenous population.

Japan continued to assert control over the islands even after withdrawing from the League in 1933. However, the obligations that came with the original mandate remained in force under international law. That Japan recognized this was shown by the fact that Japan continued to make annual reports on the mandates to the League until 1938.

During the 1920s, Western observers reported favorably on the zeal and energy with which the Japanese improved the island infrastructure and provided for the welfare of the native inhabitants.Japanese entrepreneurs of the South Seas Trading Company ( Nan'yō Bōeki Kaisha, or Nambō for short) had already gained control of much of the trade in the islands even before the First World War, and they became the vanguard for further economic penetration. The few mission schools were displaced by government schools that taught the Japanese language and respect for Japanese culture. The oldest generation of natives, interviewed by Peattie in the 1980s (Myers and Peattie 1984), recalled that the Japanese schools were effective at leading the students to think of Japan as their nation. However, the Micronesians were never considered Japanese nationals, and the Mandates were placed under the Greater East Asia Ministry rather than the Home Ministry after the Colonial Ministry was abolished in 1942.

The initial attempts to establish a sugar industry ended in near disaster, largely because the investors knew little about sugar cultivation, and at a high human cost to the immigrant farmers involved. Most were tenant farmers from Okinawa or the impoverished Tōhoku region of Japan, who found themselves stranded in the tropics when funds ran out. However, by 1925 the sugar industry was on a solid footing in the Marianas, where "sugar had indeed become king" (Myers and Peattie 1984).

This picture changed in the 1930s, as Japanese immigrants began to outnumber the native population, the natives found their lives increasingly regimented by Japanese officials, and the Japanese became secretive about their activities. Japan invested fairly heavily in some of the islands (some $28 million, equivalent to almost a billion 2009 dollars, by June 1941) and established important bases, but, contrary to rumor, construction of fortifications did not begin until just before war broke out. These rumors may have been deliberately encouraged by the Japanese, who very closely controlled access to the islands.

In fact, the Japanese were scrupulous about observing the non-fortification pledge until withdrawing from the League of Nations in 1933.  Between 1933 and 1939 the Navy began encouraging harbor improvements, airfield construction, establishment of fuel dumps, and other construction that was plausibly civilian in character but had obvious military value. With the outbreak of war in Europe in late 1939, the Japanese abandoned its nonfortification pledge and organized 4 Fleet at Truk. Even then, construction of bases and fortifications took place at a very leisurely pace. The islands were regarded as expendable in a war against the United States, and base development was limited to the minimum required to support the attrition strategy dictated by Decisive Battle Doctrine.

This doctrine was overtaken by events, and by 1943, construction of fortifications was well along. The Japanese military was able to recruit a number of Micronesian volunteer units, or teishintai.  However, the newly arrived Japanese garrison troops, who were unfamiliar with Micronesian culture and disinclined to take the time to learn,alienated much of the previously friendly native population.

The U.S. Marines subsequently paid a steep price to wrest some of the islands away from Japan. The civilian population of the bypassed atolls also paid a heavy price, as the Japanese military left them to shift for themselves. Many were reduced to grubbing for roots and hunting rats to stave off starvation.

Other Mandated Territories. The Japanese were not alone in receiving Class C mandates in the Pacific. Australia was mandated the northeast portion of New Guinea, which had formerly been German territory. New Zealand was granted a Class C mandate over Nauru and western Samoa. Neither of these British Dominions made any particular effort to extensively develop, let alone fortify, either area.


Dorn (accessed 2007-11-27)

Miller (1991)

Morison (1951)

Myers and Peattie (1984)

Venzon (2003)

Zimm (2011)

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