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Russo-Japanese War
(1904-05), military conflict in which a victorious Japan forced Russia to abandon its expansionist policy in the Far East, becoming the first Asian power in modern times to defeat a European power. 
The Russo-Japanese War developed out of the rivalry between Russia and Japan for dominance in Korea and Manchuria. In 1898 Russia had pressured China into granting it a lease for the strategically important port of Port Arthur (now Lü-shun), at the tip of the Liaotung Peninsula, in southern Manchuria. Russia thereby entered into occupation of the peninsula, even though, in concert with other European powers, it had forced Japan to relinquish just such a right after the latter's decisive victory over China in the Sino-Japanese War of 1894-95. Moreover, in 1896 Russia had concluded an alliance with China against Japan and, in the process, had won rights to extend the Trans-Siberian Railroad across Chinese-held Manchuria to the Russian seaport of Vladivostok, thus gaining control of an important strip of Manchurian territory. 
However, though Russia had built the Trans-Siberian Railroad (1891-1904), it still lacked the transportation facilities necessary to reinforce its limited armed forces in Manchuria with sufficient men and supplies. Japan, by contrast, had steadily expanded its army since its war with China in 1894 and by 1904 had gained a marked superiority over Russia in the number of ground troops in the Far East. After Russia reneged in 1903 on an agreement to withdraw its troops from Manchuria, Japan decided it was time to attack. 
The war began on Feb. 8, 1904, when the main Japanese fleet launched a surprise attack and siege on the Russian naval squadron at Port Arthur. In March the Japanese landed an army in Korea that quickly overran that country. In May another Japanese army landed on the Liaotung Peninsula, and on May 26 it cut off the Port Arthur garrison from the main body of Russian forces in Manchuria. The Japanese then pushed northward, and the Russian army fell back to Mukden (now Shen-yang) after losing battles at Fu-hsien (June 14) and Liao-yang (August 25), south of Mukden. In October the Russians went back on the offensive with the help of reinforcements received via the Trans-Siberian Railroad, but their attacks proved indecisive owing to poor military leadership. 
The Japanese had also settled down to a long siege of Port Arthur after several very costly general assaults on it had failed. The garrison's military leadership proved divided, however, and on Jan. 2, 1905, in a gross act of incompetence and corruption, Port Arthur's Russian commander surrendered the port to the Japanese without consulting his officers and with three months' provisions and adequate supplies of ammunition still in the fortress. 
The final battle of the land war was fought at Mukden in late February and early March 1905, between Russian forces totaling 330,000 men and Japanese totaling 270,000. After long and stubborn fighting and heavy casualties on both sides, the Russian commander, General A.N. Kuropatkin, broke off the fighting and withdrew his forces northward from Mukden, which fell into the hands of the Japanese. Losses in this battle were exceptionally heavy, with approximately 89,000 Russian and 71,000 Japanese casualties. 
The naval Battle of Tsushima finally gave the Japanese the upper hand in the conflict. The Japanese had been unable to secure the complete command of the sea on which their land campaign depended, and the Russian squadrons at Port Arthur and Vladivostok had remained moderately active. But on May 27-29, 1905, in a battle in the Tsushima Straits, Admiral Togo Heihachiro's main Japanese fleet destroyed the Russian Baltic Fleet, which, commanded by Admiral Z.P. Rozhestvensky, had sailed in October 1904 all the way from the Baltic port of Liepaja to relieve the forces at Port Arthur and at the time of the battle was trying to reach Vladivostok. (See Tsushima, Battle of.) Japan was by this time financially exhausted, but its decisive naval victory at Tsushima, together with increasing internal political unrest throughout Russia, where the war had never been popular, brought the Russian government to the peace table. 
President Theodore Roosevelt of the United States served as mediator at the peace conference, which was held at Portsmouth, N.H., U.S. (Aug. 9-Sept. 5, 1905). In the resulting Treaty of Portsmouth, Japan gained control of the Liaotung Peninsula (and Port Arthur) and the South Manchurian railroad (which led to Port Arthur), as well as half of Sakhalin Island. Russia agreed to evacuate southern Manchuria, which was restored to China, and Japan's control of Korea was recognized. Within two months of the treaty's signing, a revolution compelled the Russian tsar Nicholas II to issue the October Manifesto, which was the equivalent of a constitutional charter.