Northern Zhou's basis of power was established by Yuwen Tai, who was paramount general of Western Wei, following the split of Northern Wei into Western Wei and Eastern Wei in 535. After Yuwen Tai's death in 556, Yuwen Tai's nephew Yuwen Hu forced Emperor Gong of Western Wei to yield the throne to Yuwen Tai's son Yuwen Jue (Emperor Xiaomin), establishing Northern Zhou. The reigns of the first three emperors (Yuwen Tai's sons) -- Emperor Xiaomin, Emperor Ming, and Emperor Wu were dominated by Yuwen Hu, until Emperor Wu ambushed and killed Yuwen Hu in 572 and assumed power personally. With Emperor Wu as a capable ruler, Northern Zhou destroyed rival Northern Qi in 577, taking over Northern Qi's territory. However, Emperor Wu's death in 578 doomed the state, as his son Emperor Xuan was an arbitrary and violent ruler whose unorthodox behavior greatly weakened the state. After Emperor Xuan's death in 580 (when he was already titularly retired emperor (Taishang Huang), Emperor Xuan's father-in-law Yang Jian seized power, and in 581 seized the throne from Emperor Xuan's son Emperor Jing, establishing Sui. The imperial Yuwen clan, including the young Emperor Jing, was subsequently slaughtered by Yang Jian.
^Rein Taagepera "Size and Duration of Empires: Growth-Decline Curves, 600 B.C. to 600 A.D.", Social Science History Vol. 3, 115-138 (1979)
^In 580, after Emperor Xuan's death, the general Yuchi Jiong, believing that the regent Yang Jian was about to seize the throne, rose against Yang and declared a son of Emperor Wu's brother Yuwen Zhao (宇文招) the Prince of Zhao, whose name is lost to history, emperor, but as Yuchi was soon defeated, and nothing further was known about the emperor that he declared, that son of Yuwen Zhao is usually not considered an emperor of Northern Zhou.