After Cao Cao defeated Zhang Lu in 215, Hanzhong belonged to Wei. If Liu Bei could not take the basin, the north gate of Yi stayed in enemy hands and Guanzhong could press south. From 217 Liu Bei went to Hanzhong himself. Fa Zheng and others urged him to use the gaps in Xiahou Yuan’s line.
In 219 Huang Zhong’s troops killed Xiahou Yuan at Dingjun Mountain. Cao Cao came in person to push Liu Bei out and failed. Liu Bei held Hanzhong, and his followers named him King of Hanzhong. That title is the step before the imperial proclamation in Chengdu, and the name he used against Cao Pi’s Wei.
Zhao Yun, covering Huang Zhong, lowered his flags and opened the camp gates so that Cao Cao suspected an ambush. The account is in the separate biography of Zhao Yun, which Pei Songzhi quotes. It is quieter than the novel and more specific than Chen Shou’s main text. The novel makes Dingjun a fuller duel of generals. As a campaign, Hanzhong changes the map without those bouts.