The Southern Expansion Doctrine (南進論, Nanshin-ron) was a political doctrine in the Empire of Japan which stated that Southeast Asia and the Pacific Islands were Japan's sphere of interest and that the potential value to the Japanese Empire for economic and territorial expansion in those areas was greater than elsewhere.
This political doctrine was diametrically opposite that of the "Northern Expansion Doctrine" (北進論, Hokushin-ron) largely supported by the Imperial Japanese Army, which stated the same except with regards to Manchuria and Siberia. After the military setbacks at Nomonhan on Mongolian front, the Second Sino-Japanese War, and negative Western attitudes towards Japanese expansionist tendencies, Southern Expansion Doctrine superseded to procure colonial resources in South East Asia and neutralize the threat posed by Western military forces in the Pacific. The Army favored a "counterclockwise strike" while the Navy favored a "clockwise strike".
The “Southern Expansion Doctrine” was initially vaguely defined. It possibly originated during the final years of the Edo period, when the leaders of the Meiji Restoration determined that Japan needed to pursue a course of imperialism in emulation of the European nations in order to attain equality in status with the west. As the European powers were laying claim to territories ever closer to the Japanese home islands, the “Southern Expansion Doctrine” occupied an increasingly important place in Japanese policy and diplomacy from the early Meiji period.
In its initial stages, the “Southern Expansion Doctrine” focused primarily on Southeast Asia. The vast majority of Japanese emigrants to Southeast Asia in the early Meiji period were prostitutes (Karayuki-san), who worked in brothels in Malaya, Singapore, Philippines, Dutch East Indies and French Indochina. However, by the start of the 20th century, private Japanese companies became active in trade in the region, and the Foreign Ministry had established consulates in Manila (1888), Singapore (1889), and Batavia (1909). Communities of emigrant Japanese merchants arose in many areas, selling sundry goods to local customers, and large scale Japanese investment occurred especially in rubber, copra and hemp plantations in Malaya and in Mindanao in the southern Philippines.
With increasing Japanese industrialization came the realization that Japan was dependent (and thus vulnerable) on the supply of many raw materials from overseas locations outside its direct control. The need to promote trade, develop and protect sea routes, and to officially encourage emigration to ease overpopulation came simultaneously with the strengthening of the Imperial Japanese Navy, which gave Japan the military strength to project power to protect these overseas interests should diplomacy fail.
The formal annexation and incorporation of the Bonin Islands and Taiwan into the Japanese Empire can be viewed as first steps in implementation of the “Southern Expansion Doctrine” in concrete terms.
However, World War I had a profound impact on the “Southern Expansion Doctrine”. Japan was able to occupy the vast areas in the Pacific formerly controlled by the German Empire: i.e. the Caroline Islands, Mariana Islands, Marshall Islands and Palau. In 1919, these island groups officially became a League of Nations mandate of Japan and came under the administration of the Imperial Japanese Navy. The focus of the “Southern Expansion Doctrine” expanded to include these island groups (the South Pacific Mandate), the economic and military development of which came to be viewed as essential to Japan's security.
Meiji period nationalistic researchers and writers pointed to Japan's relations with the Pacific region from the 17th century red seal ship trading voyages, and Japanese immigration and settlement in Nihonmachi during the period before the Tokugawa bakufu's national seclusion policies. Some researchers attempted to find archeological or anthropological evidence of a racial link between the Japanese of southern Kyūshū (i.e. the Kumaso) and the peoples of the Pacific Islands.
In the 1920s and 1930s, the "Southern Expansion Doctrine" gradually came to be formalized, largely through the efforts of the Imperial Japanese Navy's "South Strike Group", a strategic think tank based out of the Taihoku Imperial University in Taiwan. Many professors at the university were either active or ex-Navy officers, with direct experience in the territories in question. The University published numerous reports promoting the advantages of investment and settlement in the territories under Navy control.
The Anti-London Treaty Faction (han-johaku ha) of the Treaty Faction within the Japanese Navy set up a “Study Committee for Policies towards the South Seas” (Tai Nan-yo Hosaku Kenkyu-kai) to explore military and economic expansion strategies, and cooperated with the Ministry of Colonial Affairs (Takumu-sho) to emphasize the military role of Taiwan and Micronesia as advanced bases for further southern expansion.
During 1920 the Foreign Ministry convened the Nan-yo Boeki Kaigi (South Seas Trade Conference), to promote South Seas commerce and published in 1928 Boeki, Kigyo oyobi imin yori mitaru Nan'yo (The South Seas in view of Trade and emigration). The term Nan-yo kokusaku (National Policy towards the South Seas) first appeared.
The Japanese government sponsored several companies, including the Nan'yo Takushoku Kabushiki Kaisha (South Seas Colonization Company), the Nanyo Kohatsu Kabushiki Kaisha (South Seas Development Company), the Nan'yo Kyokai (South Seas Society), and others with a mixture of private and government funds for development of phosphate mining, sugar cane and coconut industries in islands and to sponsor emigrants. (Japanese Societies) were established in Rabaul, New Caledonia, Fiji and New Hebrides in 1932 and in Tonga in 1935.
The success of the Navy in the economic development of Taiwan and the South Pacific Mandate through alliances among military officers, bureaucrats, capitalists, and right-wing and left-wing intellectuals contrasted sharply with Army failures in the Chinese mainland.
The Washington Naval Treaty had restricted the size of the Japanese Navy, and had also stipulated that new military bases and fortifications could not be established in overseas territories or colonies. However, by the 1920s, Japan had already begun the secret construction of fortifications in Palau, Tinian and Saipan.
In order to evade monitoring by the western powers, they were camouflaged as places to dry fishing nets or coconut, rice or sugar cane farms and Nan'yo Kohatsu Kaisha (South Seas Development Company) in cooperation with the Navy assumed responsibility for construction.
This construction increased after the even more restrictive London Naval Treaty of 1930, and the growing importance of military aviation led Japan to view Micronesia to be of strategic importance as a chain of “unsinkable aircraft carriers”, protecting Japan, and as a base of operations for operations in south-west Pacific.
The Navy also began examining the strategic importance of Papua and New Guinea to Australia, aware that Australian annexation of those territories was motivated in large part in the attempted to secure an important defense line.
The "Southern Expansion Doctrine" was officially adopted as national policy with the promulgation of the Toa shin Shitsujo (New Order in East Asia) from 1936 at the "Five Ministers Conference" (attended by the Prime Minister, Foreign Minister, Finance Minister, Army Minister and Navy Minister), with the resolution to advance south peacefully.
The Doctrine also formed part of the doctrinal basis of the Greater East Asian Co-Prosperity Sphere proclaimed by Prime Minister Konoe Fumimaro from July 1940. Resource-rich areas of Southeast Asia were earmarked to provide raw materials for Japan's industry, and the Pacific Ocean was to become a “Japanese lake”. In September 1940, Japan occupied northern French Indochina, and in November, the Pacific Islands Bureau (Nan'yo Kyoku) was established by the Foreign Ministry. While the events of the Pacific War from December 1941 overshadowed further development of the "Southern Expansion Doctrine", the Greater East Asia Ministry was created in November 1942, and a Greater East Asia Conference was held in Tokyo in 1943. During the war, the bulk of Japan's diplomatic efforts remained directed at Southeast Asia. The "Southern Expansion Doctrine" was brought to an end by Japan's defeat in World War II.