Zhu Tao
Li Baochen's alliance with Tian Chengsi, who controlled Weibo Circuit (魏博, headquartered in modern Handan, Hebei), would be severely tested in 775, as Tian, despite the alliance, looked down at his allies and had seized most of Xue Song's Zhaoyi Circuit (昭義, headquartered in modern Anyang, Henan) after Xue's death in 773 rather than allowing Xue's family to retain the territory. In or shortly before 775, there was an incident where Li Baozheng and Tian's son Tian Wei () were playing polo at Weibo, when an accidental collision between Li Baozheng's and Tian Wei's horses killed Tian Wei. Tian Chengsi, in anger, imprisoned Li Baozheng and sent a messenger to Li Baochen in protest. Li Baochen, wanting to be conciliatory, sent a cane back with Tian's messenger and allowed Tian to discipline Li Baozheng — but Tian, in anger over his son's death, caned Li Baozheng to death, causing Li Baochen to break off the alliance with Tian. He and Li Zhengji, who also felt slighted by Tian, submitted petitions to the imperial government asking to attack Tian, and Emperor Daizong agreed, launching troops from a number of circuits loyal to the imperial government, in addition to Li Baochen's and Li Zhengji's forces, to attack Tian. Li Baochen, Zhu Tao (whose brother Zhu Ci had killed Zhu Xicai in 772, submitted Lulong to Tang imperial authority, and went to Chang'an to serve as chancellor, leaving Zhu Tao in command of Lulong), and Xue Jianxun () the military governor of Taiyuan Circuit attacked Tian from the north, while Li Zhengji and Li Zhongchen the military governor of Huaixi Circuit (淮西, headquartered in modern Zhumadian, Henan) attacked Tian from the south. Initially, these joint forces were successful in their attacks against Tian, seizing Ci Prefecture (磁州, in modern Handan) from Tian, but Tian was subsequently able to persuade Li Zhengji to break off his attack, substantially weakening the joint forces. Meanwhile, Li Baochen was offended when an imperial eunuch, Ma Chengqian (), who had visited Li Baochen's army, was so dissatisfied with Li Baochen's gift to him that he threw it on the ground, and Tian was also able to use hoaxes to persuade Li Baochen that if he joined forces with Tian to attack Lulong, he would be successful. Li Baochen thus turned against Zhu Tao, launching a surprise attack on him, but was unable to kill Zhu Tao, effectively ending any hopes of the campaign against Tian and subsequently creating an enmity between the Chengde and Lulong Circuits. Tian subsequent ceded Cang Prefecture (滄州, in modern Cangzhou, Hebei) to LI Baochen, cementing the reformed alliance and increasing Li Baochen's holdings to seven prefectures. By 777, Li Baochen had an army that was 50,000-men strong, and Emperor Daizong created him the Prince of Longxi.