 Emperor Wu died in 578, and his son Yuwen Yun the Crown Prince succeeded him (as Emperor Xuan).In 579, Emperor Xuan passed the throne to his young son Yuwen Chan the Crown Prince (as Emperor Jing), although he held onto power as retired emperor (with the atypical title of "Emperor Tianyuan" (天元皇帝, "Tianyuan Huangdi").Later that year, Emperor Xuan made Wei Xiaokuan in charge of Xu Province (徐州, roughly modern Xuzhou, Jiangsu) and the surrounding provinces, and Wei subsequently participated in the campaign against rival Chen Dynasty that allowed Northern Zhou to seize the region between the Yangtze River and Huai River from Chen.