The First World War triggered the reorganization of world shipping. Tonnage owned in Britain and the Commonwealth, as a proportion of world tonnage, declined steadily from forty-five percent in 1914 to thirtyfive percent in 1927, while that of Japan and the US increased rapidly (see table 1). Due to reparations, Germany's ocean-going tonnage had fallen to zero by 1922, but thereafter it made a quick recovery to constitute a factor in world shipping once more. US shipping, on the other hand, was put under the control of the Shipping Board and liberalization was a slow process. Accordingly, Japan, whose tonnage had increased enormously during the war, emerged as the major growth point in the realignment of world shipping during the 1920s. As the volume of laid-up tonnage decreased significantly in 1926-1927, and world trade began to show signs of recovery, new routes were quickly developed, especially by Japanese shipping companies.

The scale of the Japanese economy expanded enormously during the 1914-1918 conflict, with the cotton spinning industry leading the way in terms of exports. Taking advantage of the absence of previously dominant British textiles in areas such as South Asia, Africa, Australia and South America, the Japanese expanded from East Asia into these under-supplied markets at one fell swoop (see table 2). Japanese shipowners first entered the Australian and South Pacific routes when conferences lost control of these trades because of the war. Then, after 1918, the Japanese, in seeking outlets for their surplus tonnage, aggressively developed routes in areas where conferences control was weak or non-existent, most notably in the Pacific, to New Zealand, and the African-South American routes. Moreover, in line with the development of Japan's heavy and chemical industries, South Pacific services were energetically cultivated as supply routes for raw materials such as rubber, tin, iron ore and soda ash. On these routes it was possible to assign ships according to cargo movements uninhibited by conferences, so that Japan was able to import from a wider range of countries. For example, raw cotton was now imported from Brazil, Egypt and Uganda in addition to India and the US, and wool was brought in from Argentina, South Africa and New Zealand as well as from Australia.