Tang's border defense forces came into open combat, even though both sides continued negotiations. In 843, the Tang general Liu Mian () launched a surprise attack against Wujie Khan, led by his officer Shi Xiong. Shi crushed Wujie Khan's forces and rescued Princess Taihe. Wujie Khan fled, and subsequently, the Huigu remnants created only minor nuisances for Tang and no longer posed a major threat. The Zhaoyi campaign Immediately after the dissipation of the Huigu threat, however, Emperor Wuzong faced a crisis of a different kind. In 843, Liu Congjian the military governor (Jiedushi) of Zhaoyi Circuit (昭義, headquartered in modern Changzhi, Shanxi), who had governed Zhaoyi in de facto independence from the imperial government and who had a strident rivalry with Qiu Shiliang, was seriously ill, and Liu wanted his adoptive son (and biological nephew) Liu Zhen to succeed him, and set up the power structure at the circuit to facilitate the transition. He submitted petitions requesting that Liu Zhen be allowed to take over the circuit. When Liu Congjian thereafter died, Liu Zhen sought to inherit the circuit. Li Deyu, believing that this would be a prime opportunity for the imperial government to seize control of Zhaoyi Circuit, advocated a campaign against Liu Zhen, and Emperor Wuzong agreed. Initially, the imperial government was concerned that three other de facto independent circuits north of the Yellow River (Weibo (魏博, headquartered in modern Handan, Hebei), then governed by He Hongjing; Chengde (成德, headquartered in modern Shijiazhuang, Hebei), then governed by Wang Yuankui; and Lulong (盧龍, headquartered in modern Beijing, then governed by Zhang Zhongwu) would side with Zhaoyi. Emperor Wuzong secured their cooperation by effectively promising the three circuits that he would not interfere with their independence, and in fact secured the military cooperation of both Weibo and Chengde in the campaign against Zhaoyi by leaving the task of capturing Zhaoyi's three eastern prefectures, east of the Taihang Mountains, to Wang and He Hongjing. The other imperial generals, including Wang Zai, Shi Xiong, and Liu Mian, concentrated on Zhaoyi's two western prefectures, including its capital Lu Prefecture (). Initially, the imperial forces could not advance well against Zhaoyi forces, and the campaign was complicated by a mutiny by the officer Yang Bian () at Hedong Circuit (河東, headquartered in modern Taiyuan, Shanxi) early in 844. Yang's mutiny was quickly put down, however, and the imperial forces continued their assault on