Wu Yuanji (吳元濟) (783[1] or 793[2] – December 12, 817[3]) 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.
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.
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.
[5] 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 imperial generals Li Guangyan the military governor of Zhongwu Circuit (忠武, headquartered in modern Xuchang) and Wu Chongyin the military governor of Heyang Circuit (河陽, headquartered in modern Pingdingshan) were having success against Zhangyi forces, but in spring 816, Zhangyi forces dealt Gao Xiayu (高霞寓) the military governor of Tangsuideng Circuit (唐隨鄧, headquartered at Tang Prefecture) a major defeat, such that Gao barely escaped with his life.
However, after the first two years, there were fewer guest soldiers, and Huaixi forces had to directly engage the regular troops of Zhongwu and Heyang Circuits.
If the central government had ordered E [(鄂州, in modern Wuhan, Hubei)], Shou, and Tang Prefectures to just protect their boundaries and not attack, and sent the Zhongwu and Zhenghua [(鄭滑, headquartered in modern Anyang, Henan)] forces, along with specialized archers from Xuan [(宣州, in modern Xuancheng, Anhui)] and Run [(潤州, in modern Zhenjiang, Jiangsu)] Prefectures to blockade Huaixi's borders, within a year, Cai Prefecture would have fallen.As Li Su was not well known, and the Zhangyi forces had defeated Gao Xiayu and Yuan Zi previously, it was said that the Zhangyi forces did not consider Li a threat and did not take much precautions against him.
Meanwhile, with Zhangyi's food supplies running low, the people were forced to initially resort to eating water caltrop, fish, freshwater turtles, birds, and beasts, but after those plants and animals ran out, the people started surrendering to the imperial forces en masse.
The Zhangyi forces, believing that detaining the people would merely lead to quicker drain on resources, did not stop them.
[7] On November 27, 815,[8] at dusk, Li Su launched an attack, from his then-base of Wencheng Fence (文成柵, in modern Zhumadian), and, after dusk, after destroying the bridges between Huiqu and Cai Prefecture, and with a major winter snowstorm serving as cover, he advanced quickly to Cai Prefecture.
Dong Chongzhi immediately abandoned his troops and returned to Cai Prefecture to surrender to Li Su.