Yamagata was born in a lower-ranked samurai family from Hagi, the capital of the feudal domain of Chōshū (present-day Yamaguchi prefecture). He went to Shokasonjuku, a private school run by Yoshida Shōin, where he devoted his energies to the growing underground movement to overthrow the Tokugawa shogunate. He was a commander in the Kiheitai, a paramilitary organization created on semi-western lines by the Chōshū domain. During the Boshin War, the revolution of 1867 and 1868 often called the Meiji Restoration, he was a staff officer.
After the defeat of the Tokugawa, Yamagata together with Saigō Tsugumichi was selected by the leaders of the new government to go to Europe in 1869 to research European military systems. Yamagata like many Japanese was strongly influenced by the recent striking success of Prussia in transforming itself from an agricultural state to a leading modern industrial and military power. He accepted Prussian political ideas, which favored military expansion abroad and authoritarian government at home. On returning he was asked to organize a national army for Japan, and he became War Minister in 1873. Yamagata energetically modernized the fledgling Imperial Japanese Army, and modeled it after the Prussian Army. He began a system of military conscription in 1873.
As War Minister, Yamagata pushed through the foundation of the Imperial Japanese Army General Staff, which was the main source of Yamagata's political power and that of other military officers through the end of World War I. He was Chief of the Army General Staff in 1878–1882, 1884–85 and 1904-1905.
Yamagata in 1877 led the newly modernized Imperial Army against the Satsuma Rebellion led by his former comrade in revolution, Saigō Takamori of Satsuma. At the end of the war, when Saigo's severed head was brought to Yamagata, he ordered it washed, and held the head in his arms as he pronounced a meditation on the fallen hero.
He also prompted Emperor Meiji to write the Imperial Rescript to Soldiers and Sailors, in 1882. This document was considered the moral core of the Japanese Army and Naval forces until their dissolution in 1945.
Yamagata was awarded the rank of field marshal in 1898. He showed his leadership on military issues as acting War Minister and Commanding General during the First Sino-Japanese War; as the Commanding General of the Japanese First Army during the Russo-Japanese War; and as the Chief of the General Staff Office in Tokyo. He was the political and military ideological ancestor of the Hokushin-ron as he traced the first lines of a national defensive strategy against Russia after Russo-Japanese War.
Yamagata was one of the group of seven political leaders, later called the genrō, who came to dominate the government of Japan. The word can be translated principal elders or senior statesmen. The genrō were a subset of the revolutionary leaders who shared common objectives and who by about 1880 had forced out or isolated the other original leaders. These seven men (plus two who were chosen later after some of the first seven had died) led Japan for many years, through its great transformation from an agricultural country into a modern military and industrial state. All the genrō served at various times as cabinet ministers, and most were at times prime minister. As a body, the genrō had no official status, they were simply trusted advisers to the Emperor. Yet the genrō made collectively the most important decisions, such as peace and war and foreign policy, and when a cabinet resigned they chose the new prime minister. In the twentieth century their power diminished because of deaths and quarrels among themselves, and the growing political power of the Army and Navy. But the genrō clung to the power of naming prime ministers up to the death of the last genrō Prince Saionji in 1940.
Yamagata and Itō Hirobumi were long the most prominent of the seven, and after the assassination of Itō in 1909, Yamagata dominated the genrō. But Yamagata also held a large and devoted power base in the officers of the army and the militarists. He became the towering leader of Japanese conservatives. He profoundly distrusted all democratic institutions, and he devoted the later part of his life to building and defending the power, especially the political power, of the army.
During his long and versatile career, Yamagata held numerous important governmental posts. In 1882, he became president of the Board of Legislation (Sanjiin) and as Home Minister (1883–87) he worked vigorously to suppress political parties and repress agitation in the labor and agrarian movements. He also organized a system of local administration, based on a prefecture-county-city structure which is still in use in Japan today. In 1883 Yamagata was appointed to the post of Lord Chancellor, the highest bureaucratic position in the government system before the Meiji Constitution of 1889.
Yamagata became the third Prime Minister of Japan after the creation of the Cabinet of Japan from December 24, 1889 to May 6, 1891. He became the first prime minister who had to share power with a partially-elected Imperial Diet under the Meiji Constitution that took effect in 1890. During his first term, the Imperial Rescript on Education was issued. In order to pass a budget for fiscal 1891 (begins in April), he had to negotiate with a liberal majority in the House of Representatives, the elected lower house of the Diet.
Yamagata became Prime Minister for a second term from November 8, 1898 to October 19, 1900. In 1900, while in his second term as Prime Minister, he ruled that only an active military officer could serve as War Minister or Navy Minister, a rule that gave the military control over the formation of any future cabinet. He also enacted laws preventing political party members from holding any key posts in the bureaucracy.
He was President of the Privy Council from 1893–94 and 1905–22.
Attending the coronation of the Russian Czar Nicholas II on November 1, 1894, Yamagata made a tentative offer to Spain on buying the Philippines for £40 million.
In 1896, Yamagata led a diplomatic mission to Moscow, which produced the Yamagata–Lobanov Agreement confirming Japanese and Russian rights in Korea.
Yamagata was elevated to the peerage, and received the title of koshaku (prince) under the kazoku system in 1907.
From 1900 to 1909, Yamagata opposed Itō Hirobumi, leader of the civilian party, and exercised influence through his protégé, Katsura Tarō. After the assassination of Itō Hirobumi in 1909, Yamagata became the most influential politician in Japan and remained so until his death in 1922, although he retired from active participation in politics after the Russo-Japanese War. However, as president of the Privy Council from 1909 to 1922, Yamagata remained the power behind the government and dictated the selection of future Prime Ministers until his death. However, his power had been greatly damaged in 1921 when he expressed strong opposition to the engagement of Hirohito and Nagako citing color blindness of Nagako's family. The Imperial family struggled against the pressure from Yamagata and the couple eventually managed to get married.
In 1912 Yamagata set the precedent that the army could dismiss a cabinet. A dispute with Prime Minister Marquis Saionji Kinmochi over the military budget became a constitutional crisis, known as the Taisho Crisis after the newly enthroned Emperor. The army minister, General Uehara Yūsaku, resigned when the cabinet would not grant him the budget he wanted. Saionji sought to replace him. Japanese law required that the ministers of the army and navy must be high-ranking generals and admirals on active duty (not retired). In this instance all the eligible generals at Yamagata's instigation refused to serve in the Saionji cabinet, and the cabinet was compelled to resign.
Yamagata was a talented garden designer, and today the gardens he designed are considered masterpieces of Japanese gardens. A noted example is the garden of the villa Murin-an in Kyoto.
As Yamagata had no children, he adopted a nephew, the second son of his eldest sister, to be his heir. Yamagata Isaburō subsequently assisted his adopted father by serving as a career bureaucrat, cabinet minister, and head of the civilian administration of Korea.Count (July 7, 1884)
Genro (May 26, 1895)
Grand Cordon of the Order of the Rising Sun with Paulownia Blossoms (August 5, 1895)
Marquis (August 5, 1895)
Marshal-General (January 20, 1898)
Collar of the Order of the Chrysanthemum (September 21, 1908) (Grand Cordon: June 3, 1903)
Grand Cordon of the Order of the Golden Kite, 1st Class (September 21, 1908) (Second Class: August 5, 1895)
Prince (September 21, 1908)
Junior First Rank (February 1, 1922; posthumous)
British Empire - Member of the Order of Merit (with swords) in 1906 by King Edward VII
British Empire - Knight Grand Cross of the Order of St Michael and St George