Hanzhong Campaign

The Hanzhong Campaign was a military campaign launched by the warlord Liu Bei to seize control of Hanzhong Commandery from his rival, Cao Cao. The campaign took place between December 217 and August 219 during the prelude to the Three Kingdoms period. Although Cao Cao's forces had settled in Hanzhong Commandery two years prior after the Battle of Yangping, they were worn out by an overall Fabian strategy employed by Liu Bei's forces, who used targeted attacks to capture strategic locations from the enemy. One of these attacks resulted in the death of Xiahou Yuan, one of Cao Cao's top generals, delivering a huge blow to the morale of Cao Cao's forces. Due to logistical and other issues, Cao Cao was eventually forced to abandon Hanzhong Commandery and order a retreat in June 219. Liu Bei emerged victorious in the campaign and occupied Hanzhong Commandery, after which he declared himself "King of Hanzhong" in August of that year.

The campaign would ultimately prove to be the final military campaign that Cao Cao participated in before his death in March of 220.

In April 215, Cao Cao attacked the warlord Zhang Lu in Hanzhong Commandery, defeating the latter at the Battle of Yangping. In December, Zhang Lu surrendered and Hanzhong Commandery came under Cao Cao's control. Afterwards, Cao Cao appointed Pu Hu (朴胡), Du Huo (杜濩) and Yuan Yue (袁約) as Administrators of the three Ba commanderies. But they were defeated by Huang Quan who then seized control of Badong (巴東), Baxi (巴西) and Ba (巴) commanderies.

On Liu Bei's side, he had also recently seized control of Yi Province (covering present-day Sichuan and Chongqing) from Liu Zhang in July 214, and was in the midst of a dispute with his ally Sun Quan over Jing Province (covering present-day Hubei and Hunan) in July 215. Liu Bei felt threatened when he received news that Hanzhong Commandery had fallen to Cao Cao, because Hanzhong was the northern "gateway" into Yi Province and he was now in danger of losing Yi Province to Cao Cao. Hence, Liu Bei came to a border treaty with Sun Quan, who had seized Changsha (長沙), Guiyang (桂陽) and Lingling (零陵) commanderies in southern Jing Province from him. Liu Bei demanded Lingling Commandery back. In return, he recognised Sun Quan's control over Changsha, Jiangxia (江夏) and Guiyang commanderies.

In Hanzhong Commandery, Sima Yi and Liu Ye urged Cao Cao to use the opportunity to attack Yi Province, but Cao Cao rejected the idea, saying, "We should not be discontent. Now that we've already conquered Longyou (referring to present-day eastern Gansu), you're still longing about merging Shu (referring to Yi Province)!" Cao Cao then left his generals Xiahou Yuan, Zhang He and Xu Huang behind to defend Hanzhong Commandery, and his Chief Clerk (長史) Du Xi to oversee the commandery's military affairs.

In December 217, Liu Bei's adviser Fa Zheng analysed the reason Cao Cao left Xiahou Yuan to guard Hanzhong Commandery and didn't push to conquer Yi province was not because of a lack of strength or insight but because he met some internal problems and was needed back at the capital. Fa Zheng also believed that Xiahou Yuan and Zhang He's ability didn't match those of Liu Bei's commanders, so the pair could not defend Hanzhong Commandery. Hence, Fa Zheng urged Liu Bei to attack Hanzhong Commandery, stating three benefits if the commandery could be taken: ideally it could serve as a base of operations to attack Cao Cao and revive the Han dynasty; if that were not possible one could still attack Yong and Liang provinces from it (Hanzhong Commandery granted access to the two provinces) and expand his territory; and finally Hanzhong Commandery had long-lasting strategical impact on the survival of Liu Bei's regime. Liu Bei agreed with Fa Zheng's analysis and ordered him to plan for the upcoming campaign.

In December 217, Liu Bei's army advanced towards Yangping Pass (陽平關). At the same time, Liu Bei also sent Zhang Fei, Ma Chao, Wu Lan (吳蘭), Lei Tong (雷銅) and Ren Kui (任夔) to attack Wudu Commandery (武都郡), and they garrisoned at Xiabian County (下辨縣). During this time, Leiding (雷定) of the Di ethnic group led seven tribes to join Liu Bei. As for Cao Cao's side, Xiahou Yuan defended Yangping Pass, Zhang He and Xu Huang respectively guarded Guangshi (廣石) and Mamingge (馬鳴閣), while Cao Hong and Cao Xiu led a separate force to resist Zhang Fei, with Cao Xiu in a nominal advisory role but in practice sharing command by Cao Cao's order.

In April 218, Zhang Fei and Ma Chao's army garrisoned at Gushan (固山), where they spread news that they were going to blockade the enemy's retreat route. Cao Hong wanted to attack Wu Lan at Xiabian County, but the other officers were suspicious of Zhang Fei's movements. Cao Xiu thought that if Zhang Fei was really planning to seal their retreat route, he should keep his plan covert; now that Zhang Fei had overtly revealed his intention, they should make use of the opportunity to feign retreat and perform a frontal assault. Cao Hong agreed to Cao Xiu's tactic and attacked in the third month. Lei Tong and Ren Kui were killed in battle, while Wu Lan fled to join the Di tribes, where he was subsequently killed by Qiangduan (強端), a Di leader of Yinping (陰平). After their subordinate's defeat, Zhang Fei and Ma Chao withdrew their army.