Background
In the autumn of 208, Sun Quan faced two wars layered atop each other: Cao Cao had driven south to Xiangyang in the eighth month and received Liu Cong's surrender along with his naval forces in the ninth month, swallowing at a stroke both the Jingzhou fleet and the Jiangxia defensive line; at the same time, Sun Quan had only just completed his spring-summer campaign against Huang Zu at Jiangxia, with Jiangdong's main forces still recuperating north of the Yangtze. Without a clear policy decided before the tenth month — and without command authority consolidated in the hands of someone who could direct all the regional commanders — Jiangdong would be forced to choose between surrender and dissolution. Zhou Yu's recall from Boyang to Chaisang was the last decision in this window.
Key Figures
Zhou Yu was thirty-four years old at the time, and since the era of Sun Ce he had been Jiangdong's most respected central protector-general; but his long years commanding troops in the direction of Wancheng had left him distant from the political networks of Jiangdong's home-grown civil official faction (Zhang Zhao, Qin Song, Lu Ji). Cheng Pu was a veteran of Sun Jian's original forces who had participated in virtually every one of the Sun clan's founding campaigns; he was the most senior in standing and the most proud in temperament. Lu Su was the author of the "Tashangce" whom Sun Quan had personally recruited from Linhuai; he was responsible for the main diplomatic thread of the alliance with Liu Bei. Sun Quan himself was twenty-seven years old and had been on the throne for only seven years. His core challenge was how to "legitimately" transfer decision-making authority into the hands of the pro-war faction at a council where the pro-surrender faction dominated the discourse — appointing a supreme commander was the answer.
Central Issue
The real question this appointment addressed was not "who will fight" but "in what command structure will we fight." Sun Quan rejected the single-commander model and instead established left and right supreme commanders plus an advisory military attaché: Zhou Yu as left supreme commander, responsible for strategy and the naval forces; Cheng Pu as right supreme commander, responsible for the infantry and the veteran generals of the north bank; Lu Su as advisory military attaché, responsible for coordinating with Liu Bei's allied forces. Above all three, Sun Quan retained ultimate adjudicating authority for himself. This structure accommodated Cheng Pu's seniority without placing him directly subordinate to Zhou Yu; it also ensured that any battlefield decision required the three-way agreement of "chief strategist (Zhou Yu) + deputy (Cheng Pu) + diplomat (Lu Su)," preventing any unilateral dictate. It also converted the political judgment of "choosing war" into a fait accompli borne by a military institution, closing off the avenue for Zhang Zhao's faction to continue the debate.
Political Consequences
The most immediate result was the opening of the Battle of Chibi in the tenth month and the annihilation of Cao Cao's forces at Wulin in the twelfth — through which Jiangdong completed its final transformation from Sun Ce's original domain into a fully independent political regime. But looking further ahead, the dual-commander framework of "left supreme commander Zhou Yu, right supreme commander Cheng Pu" became the template for Sunwu's military institutions: Lu Su's subsequent command at Luku, Lv Meng's seizure of Jingzhou, and Lu Xun's defense against Shu at Yiling all essentially replicated this structure of "chief-strategist commander + senior deputy + lord adjudicating from the rear" in different theaters. Even after Zhou Yu died at Baqiu two years later, the command triangle he established in the autumn of 208 lived on: Lu Su stepped into the left supreme commander's position, with Cheng Pu continuing on the right; for nearly the next twenty years, virtually all of Sunwu's external military operations ran on this same track.
Counterfactual
If Sun Quan had adopted a single-commander model that day — whether appointing Zhou Yu or Cheng Pu — he would have triggered passive resistance from the other side: the former would have created fractures in the Sun Jian veterans represented by Cheng Pu; the latter would have left real command of the main naval force in the hands of a general unfamiliar with water warfare. Under either scenario, Sunwu's forces on the eve of Chibi could not have achieved a unified action. Conversely, had Sun Quan yielded to pro-surrender pressure and adopted a "temporary watch-and-wait" compromise — sending Zhou Yu only to defend Xiakou without pushing north of the river — Liu Bei's position at Fankou would have rapidly collapsed; the allied forces would never have assembled, and Cao Cao's next move would not have been Chibi but a direct landing in Wu commandery. That is why what appeared to be a mere personnel appointment in the autumn of 208 in fact drove three things at once into institutional stone: "Jiangdong chooses war + alliance with Liu Bei to resist Cao Cao + dual supreme-commander system." The victory at Chibi was only its first output.