Even after the Russo-Japanese War, Manchuria remained the powder keg of East Asia. In the war's aftermath, three empires, the Qing, the Russian and the Japanese, stationed their troops in Manchuria, in a struggle for military supremacy there. There has already been a considerable amount of research on these military activities. However, previous works have not discussed them from a triangular relationship. This paper contends that the history of modern East Asia cannot be understood until one examines the shift in the military balance in Manchuria from a triangular comparative point of view. The results of such examination show that, in Manchuria, each empire was unable to establish military domination alone, and therefore needed an alliance partner. During the Xinhai Revolution, the Russia-Japan ‘alliance’ wielded overwhelming military power against China. However, after the Russian Revolution in 1917, Japan renounced cooperation with a weakened Russia and built a new partnership with China to advance the Siberian intervention. The military triangle of Russia, China and Japan was unable to create a comprehensive regional security system in Manchuria because what was established was based on mutual distrust and fear.