Japan during the Siberian Intervention

The Japanese Siberian Intervention (シベリア出兵) of 1918–1922 was the dispatch of troops of the Imperial Japanese Army to the Russian Maritime Provinces as part of a larger effort by western powers and Japan to support White Russian forces against the Bolshevik Red Army during the Russian Civil War.

Background
On August 23, 1914, Japan declared war on Germany and as a result of the treaty with Britain, Japan became a member of the Entente powers and found itself on the side of its former enemy, the Russians. In February 1917, internal discord led to the overthrow of the Tsar and the formation of a Provisional Government. The Provisional government, in turn, was overthrown in the October Revolution and the newly formed Bolshevik government signed a peace treaty with Germany. This led to the collapse of the Eastern Front.

Japanese Participation
The Japanese were initially asked by the French in 1917, to intervene in Russia but declined the request. However, in February 1918, a "Siberia Planning Committee" was formed by the Imperial Japanese Army General Staff and the Army Ministry with the aim of exploring the possibility that the Tsarist collapse was an opportunity to free Japan from any future threat from Russia by detaching Siberia and forming an independent buffer state. The Army proposed attacking on two fronts, from Vladivostok to Khabarovsk along the Amur River and also via the Chinese Eastern Railway to cut off the Russian Trans-Siberian Railway at Lake Baikal.

The Japanese government, then under the civilian leadership of Prime Minister Hara Takashi refused to undertake such an expedition and it was not until the following year that events were set in motion that led to a change in this policy. In July 1918, President Wilson asked the Japanese government to supply 7,000 troops as part of an international coalition of 25,000 troops, including an American expeditionary force, planned to support the rescue of the Czech Legion and securing of wartime supplies stockpiled at Vladivostok. After heated debate in the Diet, the administration of Prime Minister Terauchi Masatake agreed to send 12,000 troops, but under the command of Japan, rather than as part of an international coalition.

Once the political decision had been reached, the Imperial Japanese Army took over full control under Chief of Staff Yui Mitsue and extensive planning for the expedition was conducted. The Japanese eventually deployed 70,000 troops - far more than any of the other Allied powers had anticipated. Furthermore, although the Allies had envisioned operations only in the vicinity of Vladivostok, within months Japanese forces had penetrated as far west as Lake Baikal and Buryatia, and by 1920, zaibatsu such as Mitsubishi, Mitsui and others had opened offices in Vladivostok, Khabarovsk, Nikolayevsk-on-Amur and Chita, bringing with them over 50,000 civilian settlers. After the international coalition withdrew its forces, the Japanese Army stayed on. However, political opposition prevented the Army from annexing the resource-rich region. Japan continued to support White Movement leader Admiral Aleksandr Kolchak until his defeat and capture in 1920, and also supported the regime of Ataman Semenov, whose unstable government collapsed by 1922. In March and April 1922, the Japanese Army repulsed large Bolshevik offensives against Vladivostok. Public opinion in Japan mounted against the cost of the Siberian Intervention, which had absorbed over half the national budget for two years. On June 24, 1922 Japan announced that it would unilaterally withdraw from all of Russian territory with the exception of northern Sakhalin island (held until 1925), which had been seized in retaliation for the Nikolaevsk Incident of 1920 by October.

Effects on Japanese politics
Japan's motives in the Siberian Intervention were complex and poorly articulated. Overtly, Japan (as with the United States and the other international coalition forces) were in Siberia to safeguard stockpiled military supplies and to "rescue" the Czech Legion. However, the Japanese government's intense hostility to communism, a determination to recoup historical losses to Russia, and the perceived opportunity to settle the "northern problem" in Japan's security by either creating a buffer state, or through outright territorial acquisition were also factors. However, patronage of various White Movement leaders left Japan in a poor diplomatic position vis-à-vis the government of the Soviet Union, after the Red Army eventually emerged victorious from the Russian Civil War. The intervention tore Japan's wartime unity to shreads, leading to the army and government being involved in bitter controversy and renewed faction strife in the army itself. The official conduct of the Siberian Intervention would later be bitterly attacked in the Japanese Diet, with Army being accused of grossly misrepresenting the size of the forces sent, misappropriation of secret funds, and support of unsavory figures such as the "Mad Baron" Roman von Ungern-Sternberg, the ugly rumors of whose atrocities had reached the press.

Japanese casualties from the Siberian Expedition included some 5,000 dead from combat or illness, and the expenses incurred were in excess of 900 million yen.