In 798, for reasons lost to history, Wu Shaocheng, whose circuit had been renamed Zhangyi by this point, sent troops to pillage Huoshan County (霍山, in modern
Lu'an,
Anhui), belonging to Shou Prefecture (壽州, in modern Lu'an) of Huai'nan Circuit (淮南, headquartered in modern
Yangzhou,
Jiangsu), killing Huoshan's defender Xie Xiang () and occupying Huoshan. In 799, he further attacked Tang Prefecture (唐州, in modern Zhumadian), belonging to Shannan East Circuit, killing its prefect Zhang Jiayu () and eunuch monitor Shao Guochao () and capturing over 1,000 residents. When Qu Huan () the military governor of Chenxu Circuit (陳許, headquartered in modern
Xuchang,
Henan) died in the fall that year, Wu further attacked Chenxu, putting its capital Xu Prefecture under siege, although his attacks were eventually repelled. (Wu had made a secret pact with then-military governor of Xuanwu, Liu Quanliang (), to attack Chenxu together and divide its territory, but Liu died around that time as well, and Liu's successor
Han Hong refused to follow the pact and further sent troops to help the defense against Wu's attack.) In response, Emperor Dezong stripped Wu of all of his offices and ordered the circuits around his to attack him. Subsequently, Han, along with
Yu Di the military governor of Shannan East Circuit, Yi Shen () the military governor of Anhuang Circuit (安黃, headquartered in modern
Xiaogan,
Hubei), Chenxu's new military governor Shangguan Shui (), and Shou Prefecture's prefect Wang Zong (), attacked Wu together, initially enjoying some successes. However, as the imperial forces lacked a supreme commander, they did not coordinate their operations and did not look out for each other. Late in 799, for reasons unknown, the imperial forces suddenly collapsed themselves, abandoning their camp site at Little Yin River (小殷水, flowing through
Luohe,
Henan), and Wu was able to take over their supplies after they abandoned their camp. After forces sent from Chengde (成德, headquartered in modern
Shijiazhuang,
Hebei), Yiwu (義武, headquartered in modern
Baoding,
Hebei), Chenxu, and Heyang (河陽, headquartered in modern
Luoyang,
Henan) were also defeated by Wu in spring 800, Emperor Dezong commissioned Han Quanyi () the military governor of Xiasui Circuit (夏綏, headquartered in modern
Yulin, Shaanxi) as the overall commander of the forces against Wu. However, Han Quanyi was also unsuccessful against Wu and later in 800 was defeated at Wulou (五樓, in modern Zhumadian). After Wu withdrew back to Cai Prefecture in winter 800, Emperor Dezong, at the advice of the general
Wei Gao and the
chancellor Jia Dan, considered pardoning Wu. Wu also sent letters to nearby imperial eunuch messengers, requesting exoneration. Emperor Dezong thus pardoned Wu and his soldiers, restoring them to their titles. It was said that Wu, meanwhile, strengthened the resolve of the people of Zhangyi against imperial forces by showing them letters addressed to Han Quanyi that he captured in the Battle of Wulou, falsely claiming that those were requests by imperial officials requesting Han to pillage Zhangyi and seizing women to serve as the officials'
concubines. He further had his soldiers' armors be inscribed with magical writing intended to curse the imperial troops. == Resubmission to Tang rule ==