Because Japanese era names (nengō) change with the Emperor and the Imperial House split in two after 1336, the Kenmu era was counted by the two sides in two different ways. "Kenmu" is the era after the Genkō era, and it is understood to have spanned the years 1334 through 1336 before the beginning of the "Engen" era, as time was reckoned by the Southern Court; and it is concurrently said to have spanned the years 1334 through 1338 before Ryakuō, as time was reckoned by the rival Northern Court. Because the Southern Court, the loser, is nonetheless considered the legitimate one, its time reckoning is the one used by historians.