 Complete the following phrase:  In 211, Zhu Ling accompanied Cao Cao on a campaign against a coalition of warlords from the west of Tong Pass and engaged them at the Battle of Tong Pass. During the battle, Cao Cao ordered Zhu Ling and Xu Huang to lead a detachment north into Hedong Commandery to establish a bridgehead at the Puban crossing of the Yellow River so he could launch an oblique attack on Huayin County. After Cao Cao returned to Ye city in 212 following his victory at the Battle of Tong Pass, Zhu Ling remained in Changan and served as a subordinate of the general Xiahou Yuan, who continued to launch attacks against the warlords. In 215, Zhu Ling participated in the battle against the Di people in Wudu Commandery and opened the path for Cao Caos 