Wu Yuanji (吳元濟) (783 or 793 – December 12, 817) was a Chinese military general during the Tang Dynasty who tried to control Zhangyi Circuit (彰義, headquartered in modern Zhumadian, Henan) without approval from Emperor Xianzong after the 814 death of his father Wu Shaoyang, who had governed the circuit in a de facto independent manner from the imperial government. Emperor Xianzong declared a campaign against Wu, and imperial troops under Li Su were eventually able to defeat and capture him. He was delivered to the Tang capital Chang'an and executed there.
Background
The biographies of Wu Yuanji in the Old Book of Tang and the New Book of Tang conflict as to when he was born — with the Old Book of Tang indicating that he was born in 783 and the New Book of Tang indicating that he was born in 793. In any case, a major part of Wu Yuanji's life would have been spent during the time when his father Wu Shaoyang served under Wu Shaocheng the military governor (Jiedushi) of Zhangyi Circuit — who was not biologically related to Wu Yuanji but who was endeared to Wu Shaoyang and treated Wu Shaoyang as a cousin. In 809, when Wu Shaocheng was seriously ill, Wu Shaoyang killed Wu Shaocheng's son Wu Yuanqing (吳元慶) and took over control of the circuit. Then-reigning Emperor Xianzong, already engaged in a campaign against another warlord, Wang Chengzong the military governor of Chengde Circuit (成德, headquartered in modern Shijiazhuang, Hebei), was unable to act against Wu Shaoyang, and thus made Wu Shaoyang acting military governor and then military governor of Zhangyi.
Wu Yuanji was Wu Shaoyang's oldest son, and he had at least two younger brothers. While Wu Shaoyang governed the circuit, Wu Yuanji was made the acting prefect of Zhangyi's capital prefecture Cai Prefecture (蔡州).
Campaign against the imperial government
Wu Shaoyang's death and aftermaths
In 814, Wu Shaoyang died. Wu Yuanji kept Wu Shaoyang's death a secret and reported to the imperial government that Wu Shaoyang was ill; meanwhile, he took over control of the circuit. Previously, Wu Shaoyang's staff members Su Zhao (蘇兆) and Yang Yuanqing (楊元卿), as well as his officer Hou Weiqing (侯惟清), had all recommended that Wu Shaoyang go to the capital Chang'an to pay homage to Emperor Xianzong, to show submission to the imperial government, and after Wu Yuanji took over, he suspected them of betraying him. He thus killed Su and imprisoned Hou. At that time, Yang was at Chang'an, and hearing this news, he informed the chancellor Li Jifu of all of Zhangyi's strengths and weaknesses. At Yang's suggestion, the messengers that Zhangyi had sent to the other circuits were detained where they were. Further, contrary to customs that, when a major general died, that the emperor would declare a day of mourning, the imperial government did not do so, but mobilized the armies of the circuits around Zhangyi to prepare for a campaign. With these events occurring, Wu Yuanji killed Yang's wife and four sons and used their blood to paint the archery range. He made Wu Shaocheng's son-in-law Dong Chongzhi (董重質) his main strategist.
Meanwhile, with Li Jifu advocating a campaign against Zhangyi, Emperor Xianzong prepared for one. At the suggestion of another chancellor, Zhang Hongjing, Emperor Xianzong declared a day of mourning for Wu Shaoyang and sent the official Li Junhe (李君何) to Zhangyi to mourn Wu Shaoyang, to see how Wu Yuanji would react. Wu Yuanji, however, refused Li Junhe admission to the circuit, and further mobilized his army. He attacked Wuyang (舞陽, in modern Luohe, Henan) and slaughtered its population; burned Ye County (葉縣, in modern Pingdingshan, Henan); and pillaged Lushan (魯山, in modern Pingdingshan) and Xiangcheng (襄城, in modern Xuchang, Henan). Li Junhe was forced to return to Chang'an.
Initial stages
Emperor Xianzong put the general Yan Shou (嚴綬) in command of the overall operations against Zhangyi and mobilized the armies of 16 circuits. In spring 815, after some small victories against Zhangyi, Yan became careless, and the Zhangyi forces fought back, defeating him at Ciqiu (磁丘, in modern Zhumadian), forcing him to flee back to Tang Prefecture (唐州, in modern Zhumadian). The Zhangyi forces also defeated the troops from Shou Prefecture (壽州, in modern Lu'an, Anhui), forcing the prefect of Shou Prefecture, Linghu Tong (令狐通), to flee back to Shou's main city, while the Zhangyi forces slaughtered the Shou troops remaining on the border.