Although Japan suffered about 2,000 casualties in the war, fighting took place outside of the country, which remained largely unscathed. The war resulted in Japan’s acquisition of territory, economic boom, and emergence as a great power with a primary seat at the table during the signing of the Treaty of Versailles in June 1919.1 Westerns have critiqued Japan’s participation in World War I as opportunism. However, Japan deployed its navy to its limit, and earned gains from the war commensurate with its contributions.2 In balance, Japan made a strategic decision to advance its interests and provided important contributions to the Allied victory.
Japan entered the conflict to support its ally, the Great Britain. Japan and Britain signed a treaty in 1902 to defend against the threat of Russian expansion in Asia and in light of Britain’s decreasing monopoly of control of the seas.3 When Great Britain declared war against Germany on 2 August 1914, Japan mobilized its navy, of about 100 warships. On 14 August, Japan issued an ultimatum to Germany to remove its forces and surrender its territory in China and island possessions in the Pacific. Germany ignored the warning, prompting Japan’s declaration of war on 23 August, followed by a second declaration of war against Austria-Hungary on 25 August.
Japan’s leadership recognized the unfolding conflict in Europe presented both a threat against and an opportunity to advance Japan’s interests. At the outbreak of the Great War, Germany controlled the port of Tsingtao, located on the Shantung Peninsula in eastern China. Germany kept its Far Eastern squadron and garrisoned 3,500 troops and 2,500 reservists in Tsingtao. From a Japanese perspective, Germany’s victory in the war could lead to increased competition in East Asia. Japan leveraged the war as an opportunity to honor its alliance with Great Britain, act as a great power, and promote its expansionist policies. Japanese leaders considered the opportunity that the war presented as “one chance in one thousand” to increase its territory while German forces were concentrated in Europe.4
Japan’s contributions during the war initially focused on seizing German territory in the Far East. Japan led a joint Anglo-Japanese military operation, consisting of about 25,000 troops, to defeat the German forces in Tsingtao, which surrendered in November 1914. Marking a change in the character of war, the battle featured the first ever use of Japanese seaplanes, launched from an air carrier, to sink a German minelayer and bombard the German positions.5 In addition, Japan conquered German possessions in Oceania: the Caroline, Marianas, Marshall and Yap islands.
Following its territorial conquests, Japan issued its infamous “Twenty-One Demands” to China in early 1915 to secure additional privileges, such as rights to Shantung Province and extending Japan’s lease over Port Arthur in Manchuria. The demands contained a set of secret provisions that allowed Japanese control of China’s police and prohibited China from granting additional concessions to other foreign powers. After China leaked the terms, Britain and United States objected, resulting in a humiliating diplomatic setback for Japan and distrust within the alliance in the early stages of the war. In May 1915, China agreed to most of the provisions except for the secret terms.
Beyond its focus in East Asia, Japan also provided significant support to the Allies’ overall efforts. Japanese naval forces hunted German cruisers, driving them east, away from critical sea lines of communication in the Indian and western Pacific Oceans.6 British forces eventually defeated the German warships following engagements in the East Pacific near Chile and off the Falkland Islands.7
Japan provided its allies with materials as well as warships and merchant ships. It sold arms and munitions to Britain and Russia and built 12 destroyers for France, resulting in a boost to the Japanese economy as exports increased by 400 percent.8 In 1914, Japan notably returned three cruisers to Russia it had captured nine years earlier in the Russo-Japanese War. Japanese industry constructed merchant shipping for Britain and was in the process of building additional merchant ships for the United States as the war ended.
In addition, Japan defended merchant ships and troop transports. Its navy protected allied shipping in the Pacific and Indian Oceans from German commerce raiders, and escorted British Dominion (Australian, New Zealand, and Indian) and French troops from Asia to the Middle East. Japan’s deployments helped to relieve strain on the British Navy and eventually on the U.S. Navy to allow these forces to concentrate on the Atlantic theater. Japan and the United States reached a secret agreement in 1917 that provided for Japan to patrol the waters around Hawaii, allowing the United States to devote more forces to the Atlantic.9
Between early 1917 and the end of the war in November 1918, Japan expanded its operations in a first-ever deployment to the Mediterranean Sea. The cruiser-destroyer squadron provided protection to British and French troop movements and conducted antisubmarine operations. The Allies valued Japan as the “international savior of the hour.”10 At its peak, Japan deployed 17 warships, including four British destroyers and gunboats that Japanese sailors were temporarily manning. By the end of the war, the Japanese squadron escorted 788 Allied ships, safeguarded 700,000 troops to Europe for the final push on the Western Front, and took part in 34 engagements with German and Austro-Hungarian submarines.
Despite wartime cooperation, Japan’s imperialist objectives and emerging power remained a concern for British leaders.11 In late 1914, Great Britain and Japan tentatively agreed to divide the German Pacific territories between Japan and Dominion powers at the equator, despite objections by Australia and New Zealand.12 In 1917, Britain, France, and Italy secretly agreed to recognize Japan’s de facto conquest of the Shantung Peninsula and Pacific territories, having delayed making a commitment out of concern for the United States' objections to Japan’s expansion in China.13
At the end of the war, Japan secured its position as a great power and retained its conquests of German territory in China and the Pacific Islands. Following negotiations with the other victors, the Treaty of Versailles legally transferred to Japan Germany’s rights and privileges to Shantung peninsula.14 Recognizing Japan’s emerging power and threat to U.S. territory, the United States initially tried to prevent Japan’s annexation of Germany’s colonies in the Pacific.15 Japan, in turn, threatened to withdraw from the founding of the League of Nations, which was President Woodrow Wilson’s highest priority. As a compromise, the great powers agreed to a mandate system for administering former colonies, which ostensibly avoided formal annexation, but provided Japan de facto control of the German colonies in the Pacific.
The outcome of the Great War presented several setbacks to Japanese objectives. First, victory marked a shift from a European-centric to a U.S.-centric world characterized by emerging principles of self-determination, nonaggression, and free trade. Japanese leaders recognized these values as the new standards of “civilized” living, despite the potential check on their ambitions in Asia.16 Second, the United States and Great Britain rejected Japan’s proposal for a racial-equality provision in the League of Nations charter, which would have marked acceptance of Japan as a co-equal actor. Third, the defeat of Germany removed a common enemy to the Allies, and resulted in the three largest fleets in the world controlled by Britain, Japan, and the United States. Out of concern for Japan’s emerging power, Great Britain decided to allow its alliance with Japan to lapse in 1921, and it was annulled in 1923. The British feared becoming entangled in a potential war between Japan and the United States, which seemed increasingly possible. Japan eventually turned from Britain to Germany for support in naval development.17
Japan fought in the Great War to support its own interests, a motive similar to that of the other imperialist powers of the time. “For Japan, it was the departure point from a primarily agricultural to industrial state and from regional to global power.”18 Japan’s casualties were relatively minor compared to the other victors. But in balance, Japan’s timely and professional actions in the war supported the ultimate victory of the Allies.
1. Frederick R. Dickinson, War and National Reinvention: Japan in the Great War, 1914–1919 (Cambridge, MA: Harvard University Asia Center, 1999), 17.
2. Timothy D. Saxon, "Anglo-Japanese Naval Cooperation, 1914–1918," Naval War College Review 53, no. 1 (Winter 2000).
3. Saxon, "Anglo-Japanese Naval Cooperation."
4. Tadashi Nakatani, “What Peace Meant to Japan: The Changeover at Paris in 1919,” in The Decade of the Great War: Japan and the Wider World in the 1910s, ed. by Tosh Minohara, Tze-Ki Hon, and Evan Dawley (Boston: Brill, 2014), 168.
5. Saxon, "Anglo-Japanese Naval Cooperation."
6. Saxon.
7. James L. Stokesbury, A Short History of World War I (New York: Harper Collins, 1991), 81.
8. Dickinson, War and National Reinvention, 21.
9. Saxon, "Anglo-Japanese Naval Cooperation."
10. Saxon.
11. Dickinson, War and National Reinvention, 20.
12. Saxon, "Anglo-Japanese Naval Cooperation."
13. Shusuke Takahara, “The Wilson Administration and the Mandate Question in the Pacific: Struggle Among the Powers Over the Disposition of Former German Colonies,” in The Decade of the Great War: Japan and the Wider World in the 1910s, ed. by Tosh Minohara, Tze-Ki Hon, and Evan Dawley (Boston: Brill, 2014), 160–61.
14. Nakatani, "What Peace Meant to Japan," 168.
15. Takahara, "The Wilson Administration and the Mandate Question," 160-161.
16. Dickinson, War and National Reinvention, 17, 34.
17. Saxon, "Anglo-Japanese Naval Cooperation."
18. Dickinson, War and National Reinvention, 19.