 However, Chen forces could not stand against Northern Zhou's attacks, and all of the cities that they had captured from Northern Qi previously quickly fell.By new year 580, nearly all of the territory north of the Yangtze had fallen to Northern Zhou, leading to a large wave of refugees who fled across the Yangtze to Chen territory.In summer 580, Northern Zhou's Emperor Xuan died suddenly, and his father-in-law Yang Jian seized power as regent.