By summer 578, Emperor Wu was engaging in military campaigns on two fronts: against Tujue in the north and against Chen in the south. However, he suddenly grew ill and, after stopping at Yunyang, ended the attack against Tujue. He entrusted the important matters to Yuwen Xiaobo, and he soon died at the age of 35. Crown Prince Yun succeeded him (as Emperor Xuan), and by 581 Northern Zhou had fallen, its throne having been seized by Emperor Xuan's father-in-law Yang Jian.