Map Introduction

Historical Evolution of Northern Yi Province (Hanzhong, Baxi, Zitong, etc.) under Shu Han (Late Eastern Han to Shu Han Period)

I. The Situation in Northern Yi Province in the Late Eastern Han

• Geographical Scope: Northern Yi Province primarily referred to Hanzhong Commandery (modern southern Shaanxi), Baxi Commandery (modern northeastern Sichuan), Zitong Commandery (the area from modern Guangyuan to Mianyang in Sichuan), and the northern part of Guanghan Commandery (modern Deyang, Mianyang). This region was the strategic throat connecting Guanzhong and Ba-Shu, holding immense military significance.

• Period of Liu Yan and Liu Zhang's Rule (188–214 AD):

  • After becoming Governor of Yi Province, Liu Yan moved the provincial seat from Luo County (modern Guanghan) to Mianzhu, later relocating it to Chengdu due to warfare. However, the north remained a crucial military zone.
  • Zhang Lu established a theocratic regime in Hanzhong, controlling the "Way of the Rice" (Way of the Five Pecks of Rice) from Hanzhong to Ba Commandery, becoming the de facto independent power in northern Yi Province.
  • During Liu Zhang's rule, commanderies like Baxi and Zitong became defensive frontlines against the threat posed by Zhang Lu.

II. Liu Bei's Entry into Shu and the Integration of Northern Yi Province (214–219 AD)

• Liu Bei's Seizure of Yi Province (214 AD):

  • After defeating Liu Zhang in 214 AD, Liu Bei still faced the threat from Zhang Lu in the north.
  • Baxi Commandery (Langzhong) became a key military base for Liu Bei, garrisoned by generals like Zhang Fei and Huo Jun.

• The Hanzhong Campaign (217–219 AD):

  • Strategic Objective: Liu Bei contested Cao Cao for control of Hanzhong to consolidate his hold on northern Yi Province.
  • Decisive Battle:
    • Battle of Dingjun Mountain (219 AD): Huang Zhong killed Xiahou Yuan, allowing Liu Bei to seize Hanzhong.
    • Cao Cao retreated to Guanzhong. Liu Bei appointed Wei Yan to defend Hanzhong and assumed the title "King of Hanzhong."
  • Administrative Adjustments:
    • The northern part of Baxi Commandery was separated to create Badong Commandery (modern Dazhou, Wanzhou), strengthening defenses.
    • Zitong Commandery, serving as the northern gateway to Chengdu, was garrisoned by generals like Huo Yi.

III. Administration of Northern Yi Province during the Shu Han Period (221–263 AD)

• Military Defense System:

  • Hanzhong Defense Line: Wei Yan proposed the "Multiple Gates Strategy," establishing outposts beyond Hanzhong to tire invading forces.
  • Baxi and Zitong Defense Line:
    • Baxi Commandery (Langzhong) formed a secondary defensive line, where Zhang Fei and later Wang Ping repelled Cao Wei attacks.
    • Zitong Commandery (Fu County) acted as Chengdu's northern shield. Zhuge Liang established agricultural garrisons and trained troops here during his Northern Expeditions.

• Zhuge Liang's Northern Expeditions and the Role of Northern Yi Province:

  • Logistical Supply: Hanzhong and Zitong were vital hubs for transporting supplies for the Northern Expeditions. Zhuge Liang established agricultural garrison colonies like "Han and Le Cities" in Hanzhong.
  • Talent Pool: Baxi Commandery (Langzhong) produced civil officials like Qiao Zhou and Du Qiong, while Zitong Commandery (Fu County) was a source of military officers (e.g., Li Yan).

• Repeated Cao Wei Offensives:

  • 228 AD: Cao Zhen and Zhang He attacked Hanzhong but were repelled by Zhao Yun and Deng Zhi at the Ji Valley.
  • 230 AD: Cao Zhen's invasion of Shu was aborted due to heavy rains; Baxi and Zitong faced no substantial threat.
  • 263 AD: During the conquest of Shu by Zhong Hui and Deng Ai, Hanzhong fell. Jiang Wei retreated to Jian'ge. After Deng Ai's surprise crossing of the Yinping Pass, Baxi and Zitong subsequently fell.

IV. Population and Economy of Northern Yi Province

• Population Movements:

  • When Liu Bei entered Shu, he relocated part of Hanzhong's population to Chengdu, leading to depopulation in Hanzhong.
  • During Zhuge Liang's Northern Expeditions, troops were conscripted from Hanzhong and Zitong to replenish the Shu Han army.

• Economic Characteristics:

  • Agriculture: Hanzhong and Baxi Commandery (Langzhong) were crucial grain-producing areas, supporting the Northern Expeditions' logistics.
  • Salt and Iron: Zitong Commandery (Fu County) had salt wells, and Baxi Commandery (Langzhong) produced iron, providing military supplies for Shu Han.

V. Northern Yi Province after the Fall of Shu Han (Post-263 AD) * Cao Wei incorporated Hanzhong, Baxi, and Zitong into Yong and Liang Provinces, turning the region into a frontline against Eastern Wu. * During the Western Jin period, Northern Yi Province gradually became integrated into the Guanzhong economic sphere, losing its military significance from the Three Kingdoms era.

Summary

Northern Yi Province was the core of Shu Han's military defense. The Hanzhong Campaign solidified its strategic position, and Zhuge Liang's Northern Expeditions relied heavily on its resources. Repeated Cao Wei offensives failed to break through its defenses until it ultimately fell due to internal weaknesses and Deng Ai's surprise attack. The historical evolution of this region profoundly influenced the tripartite balance of the Three Kingdoms period.