Regnal year dating
The tradition of Korean era names survives in the North Korean Juche calendar, with Juche year 1 being 1912 the year of the birth of Kim Il-sung.The official Japanese system or Nengō numbers years from the accession of the current emperor, regarding the calendar year during which the accession occurred as the first year.It could last from one year to the length of the leader's reign.If it lasted more than one year, numbers were appended to the era name.
Applying this ancient epoch system to modern calculations of time, which include zero, is what led to the debate over when the third millennium began.An example of this is, that when the Yongle emperor usurped the thrown from his nephew he dated the year of his accession as "洪武三十五年", the 35th year of his father, the Hongwu Emperor's reign, i.e. Hongwu had in fact died in 1398, and the short reign of the Jianwen Emperor, who ruled between 13 was written out of the official record. The short lived Daxi kingdom, post Zhang Xianzhong, used the Ganzhi calendar without era names.Overseas Chinese used Longfei (龍飛) or Tianyun (天運).The Chinese eras or Nian Hao were used sporadically from 156 BC and continuously from 140 BC.Until 1367 AD several were used during each emperor's reign.