Revolutionary change of era

…The use of era names in Japan began in the Taika era in 645, but there were intermittent periods after that, and they were used continuously from the Taiho and Keiun eras in the early 8th century onwards, and it is thought that the era name change ceremony was also institutionalised around this time. There are roughly four reasons for era name changes: (1) era names for the beginning of a new era, (2) era names for auspicious reasons, (3) era names for disasters, and (4) era names for revolutions. (1) is used when the throne is replaced by a new emperor due to his death or abdication, and is also known as an enthronement era name. …

*Some of the terminology used in reference to the "revolutionary era change" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…日本における年号の使用は645年の大化に始まるが，その後断続があり，継続的に使用されるのは8世紀初頭の大宝，慶雲以降であって，改元行事もこのころから制度化したと考えられる。改元の理由にはおおよそ(1)代始（だいはじめ）改元，(2)祥瑞（しようずい）改元，(3)災異改元，(4)革命改元の4種がある。(1)は天皇の死もしくは譲位によって帝位の交代が行われた際のもので，即位改元ともいう。…

※「革命改元」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報