Russo-Japanese War, 1904–5, imperialistic conflict that grew out of the rival designs of Russia and Japan on Manchuria and Korea. Russian failure to withdraw from Manchuria and Russian penetration into N Korea were countered by Japanese attempts to negotiate a division of the area into spheres of influence. The Russian government, however, was inflexible, and it was willing to risk an armed conflict in the belief that Japan was bound to be defeated and that a Russian victory would head off the growing threat of internal revolution in Russia. Japan broke off negotiations and severed (Feb. 6, 1904) diplomatic relations with Russia. Two days later, without a declaration of war, Japan attacked Port Arthur and bottled up the Russian fleet. A series of quick Japanese victories, which astounded the world, culminated in the fall of Port Arthur (Jan., 1905), the victory of troops under General Oyama at Shenyang (Feb.–Mar., 1905), and the destruction of the Russian fleet under Rozhdestvenski at Tsushima by Admiral Togo's fleet (May, 1905). Through the mediation of U.S. President Theodore Roosevelt, peace was made in September at Portsmouth, N.H. (see Portsmouth, Treaty of). The disastrous outcome of the war for Russia was one of the immediate causes of the Russian Revolution of 1905. Japan gained the position of a world power, becoming the first non-European and non-American imperialist modern state.
See I. Nish, The Origins of the Russo-Japanese War (1985); J. N. Westwood, Russia against Japan (1986).