Background
From the perspective of political history, the Wu–Shu pact of the first year of Huanglong (229) was not an isolated diplomatic event but the final crystallization of six years of diplomatic effort since Deng Zhi's mission to rebuild the alliance in the first year of Jianxing (223). In 223, Liu Bei died at Baidicheng and the wounds of Yiling had not yet healed; Zhuge Liang dispatched Deng Zhi to Wu to initiate a strategic rebalancing. Over the following six years, Shuhan mounted several campaigns toward Qishan while Wu contained the southern mountain tribes and harried Hefei in the north — the two states had in practice developed a tacit division of labor on the battlefield. When Sun Quan formally proclaimed himself emperor in 229, the problem Shuhan faced was not "whether to sever the alliance" but "how to accommodate a new emperor within its own narrative of legitimacy." Chen Zhen's dispatch as Palace Defender to serve as envoy was not a routine mission — the Palace Defender was the senior officer in charge of palace guards; sending an official of that rank to congratulate a coronation was itself a powerful signal of recognizing the other party's imperial system.
Key Figures
Zhuge Liang was the core decision-maker on the Shuhan side. When the later lord and his ministers deliberated, the prevailing view was that "Sun Quan has usurped the throne; we should sever the alliance" — the response consistent with Confucian orthodox doctrine — but Zhuge Liang held to the opposite course. Sun Quan's role was more visibly calculated in terms of practical interest: his choice to proclaim himself emperor at Wuchang rather than Jianye was to be closer to the front line of anti-Wei operations; his choice to formally partition territories with Shu in the same year as his proclamation was to lock in both parties' coordination through a treaty. Chen Zhen himself, though his biography in the San Guozhi is brief, bore an assignment of the highest sensitivity: he had to complete the public ceremony of a covenant oath at a sworn altar, while also privately conveying Zhuge Liang's core position of willingness to recognize Sun Quan's imperial title — making him one of the very few figures in Shuhan's diplomatic corps capable of acquitting himself in a situation of such delicacy.
Core Issues
This pact raised, at the level of political theory, the most audacious proposition of the San Guo period: that "legitimate sovereignty" could be simultaneously claimed by two emperors. In the political tradition inherited from the Han, "heaven has no two suns; the people have no two kings" was an inviolable principle; Shuhan, styling itself "the legitimate continuation of the Han dynasty," should in theory have repudiated any other imperial title. Zhuge Liang's choice was in fact to subordinate ideology to strategy — recognizing Sun Quan's imperial title in exchange for real cooperation in the joint campaign against Wei. Behind this was a thoroughly mature form of realism: the ultimate arbiter of legitimacy is the victor, not the contemporary debate; rather than fighting zero-sum on the ideological plane, it was better to first cooperate on the battlefield to jointly weaken the common enemy. This line of thought holds profound implications for multi-polar diplomacy in later history.
Political Consequences
Looking at the treaty's text, the pact stipulated that Yu, Qing, Xu, and You provinces would belong to Wu, while Yan, Ji, Bing, and Liang would belong to Shu, with Si province divided along the line of the Hanguguan Pass — a partition with several features worth analysis. First, the four provinces allocated to Shuhan lay geographically to the northwest and north of Caowei, consistent with the offensive axis of advancing from Hanzhong through the Qin Mountains. Second, the four provinces given to Wu were concentrated in Caowei's east and northeast, consistent with an offensive thrust from the Hefei and Xuzhou directions. Third, Si province, where the imperial capital was located, was split in half, ensuring both parties had a candidate for the future dynastic seat while pre-empting disputes over future spoils. This geographic design was rational in conception, but in practice neither party ever actually fought its way to the stipulated boundaries. In terms of strategic effect, the pact's most important political consequence was not the territorial division but the provision to Shuhan of a stable eastern rear for its subsequent five northern campaigns — Sunwu's continuous pressure against Caowei at Hefei meant Caowei could never concentrate its forces westward.
Counterfactual Analysis
Had Shuhan heeded its ministers and refused to recognize Sun Quan's imperial title, what would have happened? The most likely outcome would have been Wu turning to reconcile with Caowei — Sunwu had twice submitted to Caowei as a vassal in the 220s, and had technical precedent for this. Had that occurred, Shuhan would have faced the entire north alone; Zhuge Liang's northern campaigns would have been deprived of any strategic echo, and he would even have had to worry about Wu forces ascending the Kui Gorge from the southeast. Conversely, had Sun Quan delayed his imperial proclamation indefinitely without demanding recognition, the alliance could have maintained the status quo — but Sun Quan's proclamation was a domestic political necessity for Wu that could not be indefinitely deferred for diplomatic considerations. Seen from this angle, Zhuge Liang's decision had almost no alternative: it was an "expensive premium" paid at ideological cost but strategically unavoidable. It is precisely for this reason that the Wu–Shu pact is regarded by later generations as the most instructive case of alliance diplomacy in the San Guo period.