In order to prepare for a potential war against Qi and Chu, a new system was instituted such that each qiu (丘), an administrative unit roughly translatable to "district," must produce an armored soldier.
Du Yu noted in his annotations of the Zuo Zhuan that according to the Rites of Zhou, each dian (甸), which contains four qius, should supply three armored soldiers, meaning that this new policy represents an increase in taxation.
Lupu Jiukui [zh], a favorite of the Duke of Qi, scaled the walls of Lu, but was captured by the defending soldiers.
Even though the Duke of Qi plead for his life in exchange of withdrawal from Lu, the defending soldiers executed Lupu Jiukui and hanged his naked body on the city wall.
Duke Cheng commanded Minister Zang Xuanshu [zh] to sue for peace, but he refused, positing that the Chu army would leave quickly after traveling to Lu from afar, and that going to the Chu army to negotiate for peace would be accepting the credit without merit.
Then, Duke Cheng swore a covenant with Prince Yingqi of Chu [zh], with multiple representatives from nearby states attending.
In fall of the same year, Minister Shusun Qiaoru, Count Xuan of Shusun [zh], entered the land gained in the prior year to establish Lu rule there, but his army met resistance at the city of Ji (棘), forcing him to lay siege to it.
Jisun Xingfu, Viscount Wen of Ji [zh], a Lu minister, said to Duke Cheng,This will not do.
In autumn 585 BC, under the order of Jin, Duke Cheng sent Zhongsun Mie and Shusun Qiaoru to invade Song.
During the meeting, Jisun Xingfu questioned the virtue of the Duke of Jin to Jin Minister Shi Xie, Viscount Wen of Fan [zh], who replied,To care for other domains assiduously, to treat them leniently, to control them firmly, to invoke bright spirits to deter them, to deal gently with the submissive, and to attack those with divided allegiance—these are the next best things after virtue.
The Zuo Zhuan explains that this is because the leaders of Lu, considering the Duke's attendance and detainment a disgrace, decided not to record these events.
When Duke Cheng made no direct response, Mu Jiang, angry, threatened to depose him and install one of his younger brothers to the Lu throne.
In autumn 575 BC, Duke Cheng met with the rulers of Jin, Qi, and Wey as well as representatives from Song and Zhu at Shasui (沙隨) to plan an attack against Zheng (which was aligned to Chu at that time).
Shusun Qiaoru sent an envoy to Xi Chou, claiming that the Jisun and Mengsun clans intended to align Lu to Chu and Qi.
He further requested him to detain and kill Jisun Xingfu, who had been in Duke Cheng's army, while he would take care of Zhongsun Mie in Lu.
Duke Cheng, after his return to Lu, sent Prince Yingqi, Count Sheng of Zishu [zh][a], to Jin to negotiate Jisun Xingfu's release.
During the negotiations, Xi Chou promised Prince Yingqi that after removing Jisun Xingfu and Zhongsun Mie, he would be allowed total control of Lu and enjoy closer relationships to him than even Duke Cheng.
Even after Xi Chou further promised a settlement in Lu, Prince Yingqi refused to change his position.