This made the crown prince unhappy. Around the new year 574, Emperor Wu gathered Confucian scholars, Taoist monks, and Buddhist monks, and had them debate about their philosophies. He ranked Confucianism the highest, then Taoism, and then Buddhism. Subsequently, in summer 574, he banned both Taoism and Buddhism, ordering their monks to return to secular life. He also banned the worship of minor deities whose cults were not registered with the government. (This became known as the second of the Three Disasters of Wu)  In spring 574, Empress Dowager Chinu died. Emperor Wu mourned for more than a month, eating only a small amount of rice during this period. In fall 574, while Emperor Wu was at Yunyang (雲陽, in modern Xianyang, Shaanxi), Yuwen Zhi, who had long resented not receiving more authority, rebelled at Chang'an. The official Yuchi Yun (), one of the officials in charge of the capital along with Crown Prince Yun, defeated Yuwen Zhi, forcing him to flee. Yuwen Zhi was soon captured and executed. Believing Northern Qi to have been substantially weakened not only by Hulü's death but also by the successful campaign that Chen waged against it in 573 (capturing the provinces between the Yangtze River and the Huai River), by 575, Emperor Wu was seriously considering a major campaign against Northern Qi. However, he kept the matter secret, consulting only Yuwen Xian, Wang Yi (), and Yu Yi (). Only until he was ready in fall 575 did he announce it generally. He aimed his attack at Luoyang, but he spent about 20 days sieging it and could not capture it, and became ill. He withdrew, with virtually no gain. In spring 576, pursuant to Emperor Wu's orders, Crown Prince Yun launched a campaign against Tuyuhun; a campaign that appeared to be moderately successful. Yet the campaign would bring another deterioration of the relationship between father and son, as Wang Gui, who officially served as the crown prince's lieutenant (along with Yuwen Xiaobo) but was in charge of the operation, reported a matter of immoral acts that the crown prince and his associates Zheng Yi () and Wang Duan () engaged in. Emperor Wu himself caned the crown prince and his associates, expelling the associates from the crown prince's palace. (Crown Prince Yun, however, soon recalled his associates.)