Beginning in 1868, the Meiji Restoration was the major change in Japanese governance coming from the end of the Tokugawa Shogunate not only restoration of the monarchy, under Mutsohito, known as Emperor Meiji, son of the powerless Emperor Komei, as the real head of state. It ended in 1912 with Mutsohito's death. His son, Yoshihito (the Taisho Emperor), succeeded him, but was sickly, and the Emperor had little effect until Meiji's grandson, Hirohito, acceded to the Throne in 1921.
It also reformed the government itself, modernizing from feudal to technical-bureaucratic. The Restoration ended the power of the samurai class and the development of a national military. It went beyond Meiji himself, and to successive emperors, beginning with the sickly Yoshihito, and then to Yoshihito's son Hirohito. The emperor-state created ended in 1945 with the surrender of Japan in World War Two in the Pacific, although Hirohito's son, Akihito, is now a symbolic head of state.
The emperor embodied the Japanese ideal of kokutai, or a national polity for whom the Emperor was the symbolic father of the nation. Preservation of kokutai and the Throne was the only real condition the Japanese required in their surrender.
Opposition to the Tokugawa had been especially strong in the Chosu Clan, and to a lesser extent the Satsuma Clan. In 1864, Aritomo Yamagata was among the first members of the mixed rifle units (shotai) formed by Shinsaku Takasugi of the Chosu Clan, the first non-samurai combat units. Initially, he saw the shotai, or the kiheiti "shock troops" under which they were organized, as a weapon against militarily superior foreigners. Increasingly, however, he became opposed to the Tokugawa Shogunate, becoming a member of the Choshu shishi ("men of spirit") who wanted to restore Emperor rule and break the shogunate. 
Beginnings of the Cabinet
After serving as "taifu (senior vice minister) of Army-Navy Ministry, and army taifu, he became war minister in 1873. Promoting conscription, he focused on building the military system. He became chief of the General Staff Office in 1878, Home Minister in 1883, and home minister in the first Ito cabinet in 1885."
In 1877, some Satsuma samurai, angry about the Emperor's edict that only members of the military sjould wear swords, Takamori Saigo led the Satsuma Rebellion. Saigo, only shortly before, had been a leader of the Meiji government, along with Toshimichi Okubo, another Satsuma, and Koin Kido of the Chosu. Kido was a diplomat and negotiator, who convinced the feudal lords to join the national government. Saigo was the military leader and Okubo a planner. Although the 15,000 man army, quickly took Kagoshima, the Western-trained new army, directed by Toshimichi Okuba and under the tactical control of Aritomo Yamagata, defeated them,  and Saigo, badly wounded, ordered his most loyal retainer, Shinsuke Beppu, to kill him. Saigo is still revered as the "last samurai", and statues in Tokyo's Ueno Park and Kagoshima's Central Park honor him.
A major accomplishment of the Meiji era was the promulgation of a formal Constitution, granted by the Emperor in 1889, and drafted by Hirabumi Ito. Senior officials had been sent to the U.S. and Europe in 1871-1873, to study their systems. Taisuke Itagaki was acting head of government during these missions.
Conceptually, it was a gift of the Throne to the people, although it would be a living document. The Emperor had to initiate amendments, but they needed the consent of both houses of the Diet. The Diet was a bicameral national assembly, partially elective in the lower house, but certainly not a full democratic legislature. 
To advise the emperor in his proposals, the Privy Council (Japan) was formed. Much of the document enumerated the powers of the Emperor as head of state; it was not liberalizing but a formalization of the status quo.
At that time, the institution of the genro, or "elder statesmen", an extraconstitutional advisory group whose assent was necessary for any important decisions. The best-known of these were Ito, Aritomo Yamagata, and Kinmochi Saionji. They protected the emperor by making decisions in his name, and protecting him personally from criticism. 
Below the emperor and the oligarchs was a loosely western-style cabinet under a Prime Minister of Japan. At first, the cabinet members were little more than a rotation of the genro. Soon, however, a modern civil service was created, primarily on the German model, and staffed, preferentially, by graduates of Tokyo University.
Among the goals of establishing a constitution was, in turn, establishing a legal code and judicial systems under which Western powers might waive extraterritoritality. It was decde that the French civil code should be translated, a job given to a young Japanese legal scholar, Mitsukuri Rinsho. The major developer of the criminal code, promulgated in 1880, was a French adviser, Emile Gustave Boissonade de Fontarabie. Still, before it was accepted there were arguments for the English Common Law, and, finally, the major theories were Prussian Rechtstaat principles, influenced by Hermann Roesler. The first full civil code was ready in 1898.
The first four years of the Diet, however, were confrontational; the framers had not foreseen the rapid growth of the industrial and financial sectors, the influence of newspapers, widespread education, and the development of a white collar class. It the first elections, the Diet attacked the government as a "domain clique" from Chosu and Satsuma. A compromise worked out by 1900, with formation of Seiyukai, which was a political party but a political party in sympathy with the establishment government. Still, between 1901, the Prime Ministership alternated between Kinmochi Saionji and Taro Katsura. 
- Merion and Susie Harris (1991), Soldiers of the Sun: the Rise and Fall of the Imperial Japanese Army, Random House, pp. 12-14
- Edwin P. Hoyt (1985), The Militarists: the Rise of Japanese Militarism since WWII, Donald I. Fine, ISBN 0917657179
- Ivan Morris, "The Apotheos of Saigo the Great", The Nobility of Failure
- Edwin O. Reichshauer (1977), The Japanese, Harvard University Press, p. 89
- Jerrold M. Packard (1987), Sons of Heaven: A Portrait of the Japanese Monarchy, Macmillan, p. 222-223
- Packard, p. 224
- Reichshauer, p. 88
- Karel van Wolferen (1989), The Enigma of Japanese Power: People and Power in a Stateless Nation, Alfred E. Knopf, p. 208
- Reichshauer, pp. 91-92