Background
In the fourth month of the seventh year of Jianxing (229), Sun Quan formally proclaimed himself emperor at Wuchang, naming his state Wu and adopting the reign title Huanglong. This act carried epoch-making significance within the San Guo configuration: from this point, three emperors simultaneously proclaimed themselves the legitimate ruler of China — Caowei in the Central Plains, Shuhan in Yizhou, and Sunwu in Jiangdong. For Shuhan, this posed an extremely sensitive diplomatic question: Shuhan had founded its state on the banner of "the legitimate line of the Han dynasty" and in principle should not have recognized the imperial title of any other regime; yet Sunwu was Shuhan's sole strategic partner against Caowei, and refusing to recognize Sun Quan's imperial title was tantamount to severing the alliance. In the court deliberations, Zhuge Liang decisively chose the "pragmatic priority" stance — dispatching Grand Steward Chen Zhen carrying a state letter to Wuchang, formally acknowledging Sun Quan's imperial throne and using the occasion to conclude a comprehensive alliance treaty.
Content of the Oath
The treaty reached after extensive consultations between Chen Zhen and Wu representatives at Wuchang is a document of remarkable character in the history of ancient Chinese diplomacy. Its core clauses were organized in three tiers. The first tier was a mutual and equal recognition of both imperial titles — explicitly stating "the two rulers of Han and Wu share one heart in unification," pledging non-aggression and that neither would shelter the other's defectors. The second tier was a pre-emptive partition of the future Central Plains territories to be conquered from Caowei — with the Hangu Pass as the boundary, Xuzhou, Yuzhou, Qingzhou, and Youzhou would belong to Wu, while Yanzhou, Jizhou, Bingzhou, and Liangzhou would belong to Shu, with Sizhou (containing Luoyang) divided east and west at the Hangu Pass to be shared jointly by the two states. The third tier comprised military coordination clauses — "joining forces with one heart, together attacking the Wei bandits," with both parties supporting each other during campaigns against Wei. The oath text closed with the standard oath formula "if any should violate this covenant, may the gods strike them down." The particular feature of this treaty was that it pre-allocated property rights over territorial conquests that had not yet occurred, thereby eliminating the most common source of suspicion between allies — the problem of dividing the spoils after victory.
Subsequent Impact
In the short term, the greatest effect of Chenzhenwuchangmengshi was to free Zhuge Liang's Third (230), Fourth (231), and Fifth (234) Northern Expeditions from anxiety about the eastern flank. In the subsequent campaigns at Qishan, Lucheng, and Wuzhangyuan, Zhuge Liang could deploy all his elite troops westward without fear of a Wu attack from the east; Sunwu's multiple simultaneous northern campaigns against Hefei also forced Caowei to split its forces on two fronts. In the medium term, although the treaty's "partition of provinces" clauses were a long-term vision, they profoundly shaped the strategic imagination of both Wu and Shu — both states accepted the complete destruction of Caowei as the long-range objective. In the long term, neither side publicly abrogated the treaty until the successive fall of both states, making it the most durable and stable diplomatic compact of the San Guo period. Chen Zhen himself was promoted to Marquis of Chengyangting as a result of this successful mission, becoming a landmark figure in the history of Shuhan diplomacy. Even as late as the Yanxi and Jingyao periods of Shuhan, during Jiang Wei's many northern expeditions, the Wu side continued to observe the formal requirements of the treaty, demonstrating that this document exerted real constraining force far exceeding ordinary diplomatic language. From a broader perspective, Chenzhenwuchangmengshi was an early precedent of "equal treaties concluded between divided empires" in Chinese history, which had an indirect shaping effect on the diplomatic discourse of later eras of multi-polarity such as the Northern and Southern Dynasties and the Liao-Song period — demonstrating that in an era of fragmentation, mutually exclusive ideological claims can be set aside through the precise allocation of practical interests.