保元之亂
In 1156, factional divisions in the court erupted into open warfare within the capital. The cloistered Emperor Toba and his son Emperor Go-Shirakawa sided with the son of Fujiwara regent Fujiwara no Tadazane, Fujiwara no Tadamichi as well as Taira no Kiyomori (heir of the Taira clan at the time),while Cloistered Emperor Sutoku sided with Tadazane's younger son, Fujiwara no Yorinaga. This is known as the Hōgen Rebellion.