The cloistered rule or Insei system (院政) was a specific form of government in Japan during the Heian period. In this bifurcated system, an Emperor abdicated, but he retained power and influence. The emperors who withdrew to live in monasteries (in) continued to act in ways which were intended to counterbalance the influence of Fujiwara regents and the warrior class. Simultaneously, the titular emperor (the former emperor's successor) would fulfill all the ceremonial roles and formal duties of the monarch.
There were emperors who abdicated and cloistered emperors before and after the Heian period, but the cloistered rule system usually refers to the governing system put in place by Emperor Shirakawa in 1086 and remained in force until the rise of the Kamakura shogunate in 1192.
The ritsuryō code provided for abdicated emperors to exert some kind of powers. There are indeed early examples of abdicating emperors, such as Empress Jitō, Emperor Shōmu or Emperor Uda in the 7th, 8th and 9th centuries. Retired Emperor Uda was probably one of the first examples of the system, his successor Emperor Daigo being often sick.
In 1068, Emperor Go-Sanjō was the first Emperor in almost two centuries not being of Hokke Family descent. After reaching the throne, he exerted personal power while the Hokke family was dealing with internal conflicts of interests between Fujiwara no Yorimichi and his brother Fujiwara no Norimichi. He was in position to edict several laws and regulations (most notably the Enkyū Shōen Regulation Decree) during his rule, thus weakening the regency. Sick, he abdicated in 1072 in favor of Emperor Shirakawa, and died the following year. Although not having the time to exert rule by himself after his retirement, he had weakened the regency and had paved the way for the apparition of the cloistered rule.
In 1086, Emperor Shirakawa in his turn, abdicated in favor of his son, Emperor Horikawa, who was 4 at the time. The objective of the Emperor may have been to protect his young son against his own younger brother, who was a serious pretendent to the throne, but strongly exerting his personal power after his retirement he set up in effect the system and definitively weakened the regency.
End of the Heian period 
A variant Imperial court (In no Chō (院庁) evolved around the retired emperors. The will of the retired emperor was put into effect through Inzen (院宣) and In no Chō Kudashi Bumi (院庁下文). Cloistered emperors also had their own army, the Hokumen no Bushi (北面の武士). The creation of this army led to the rise in power of the Taira clan.
There was only one ruler (emperor or retired emperor), the Chiten (治天). It is important to understand that the Chiten was not ruling instead of the Emperor, but was exercising his power of patriarch of the Imperial family. The insei system can also be seen as a means of stabilization.
The Hōgen Rebellion, at the death of Toba, was nonetheless an example of direct opposition between the Emperor and the retired Emperor.
The succession of power in the Insei system was complex.
|Insei System of Imperial Rule|
|Reign dates||Emperor of Japan|| Senior
|80||1168—1180||Emperor Takakura||Go-Shirakawa||Rokujō (until 1176)|
|81||1180—1185||Emperor Antoku||Go-Shirakawa||Takakura (until 1181)|
During the Shogunates 
Usually the establishment of Kamakura Bakufu marks the beginning of Kamakura period. Yet this did not immediately end the Insei system. Though Kamakura Bakufu took over the police force and ruled Eastern Japan, the authority of Emperor and retired Emperors remained. The court and shogunate coexisted till the end of Edo period. At least at the early Kamakura period, Chiten kept substantial power over many important decisions.
However, when Go-Toba, a grandson of Go-Shirakawa and Chiten at the time, planned to overthrow Kamakura Bakufu and failed (Jōkyū War), the power of the court, particularly that of retired Emperors was markedly cut down by the shogunate.
Even after the Jōkyū War, the cloistered rule system continued to exist, at least formally, for two centuries. There were movements to take the authority back into the hands of Emperor at the throne, such as the Kemmu restoration by Emperor Go-Daigo, but in general a retired emperor presided as the head of the Kyoto court, with the approval of the Bakufu.
See also 
- Nussbaum, Louis-Frédéric. (2005). "Insei" in Japan Encyclopedia, p. 391. at Google Books
- Ponsonby-Fane, Richard. (1959). The Imperial House of Japan, pp. 257-258.
- Nussbaum, "In" at p. 385. at Google Books
- Sansom, George Bailey. (1958). History of Japan to 1334, p. 200.
- Nussbaum, "Hō-ō" at p. 351. at Google Books
- Hurst, G. Cameron. (1976). " Insei: Abdicated sovereigns in the Politics of late-Heian Japan 1086-1185.' New York: Columbia University Press. 10-ISBN 0231039328/13-ISBN 9780231039321; OCLC 1584089
- Nussbaum, Louis-Frédéric and Käthe Roth. (2005). Japan encyclopedia. Cambridge: Harvard University Press. 10-ISBN 0-674-01753-6; 13-ISBN 978-0-674-01753-5; OCLC 58053128
- Ponsonby-Fane, Richard. (1959). The Imperial House of Japan. Kyoto: Ponsonby Memorial Society. OCLC 194887
- ____________. (1956). Kyoto: The Old Capital of Japan, 794-1869. Kyoto: The Ponsonby Memorial Society. OCLC 182637732