Born Oct. 10, 1842, in the principality of Satsuma, in what is now Kagoshima Prefecture; died Dec. 10, 1916, in Fukuoka Prefecture. Japanese prince (from 1905), military figure, statesman, and marshal (1898).
Oyama came from an ancient samurai family. After the bourgeois revolution of 1867–68 (the Meiji Restoration), he played an important role in modernizing the Japanese army. During the Franco-Prussian War of 1870–71, he acquired war experience with the Prussian forces, later, from 1871 to 1874, receiving a military education in France and Switzerland. In 1877 and 1878 he took part in crushing a samurai rebellion instigated by his kinsman Takamori Saigo.
From 1885 until 1896, except for a brief interval, Oyama was minister of war. During the Sino-Japanese War of 1894–95, he commanded the Second Army, which seized Lüshun (Port Arthur). After the war, he received the title of marquis and became a member of the emperor’s privy council. From 1899 to 1904 he was chief of the general staff, and in June 1904, during the Russo-Japanese War of 1904–05, he became commander-in-chief of the ground forces in Manchuria. In 1912, Oyama became genro and lord keeper of the imperial seal.