Background
After Sun Quan Proclaims Himself Emperor, his eldest son Sun Deng was installed as crown prince and groomed over many years; the court and the realm harbored no doubts about his succession. When Sun Deng died young in the fourth year of Chiwu (241), the originally stable succession plan of Eastern Wu was thrown into disarray. The following year Sun Quan designated his third son Sun He as crown prince — a transition that could have proceeded smoothly — but he almost simultaneously enfeoffed his fourth son Sun Ba as Prince of Lu, making no distinction in ritual rank, treatment, or the configuration of personal attendants between the prince and the heir apparent. In the imperial era, the formal gap in status between the crown prince and the other princes was one of the cornerstones of dynastic stability. Sun Quan's arrangement of "two palaces standing in parallel, equal in treatment" effectively blurred the line between the legitimate heir and the others himself, sowing an institutional seed of succession conflict.
Key Figures
The true driving force behind these events was Sun Quan himself — it was he who created the situation of two palaces standing on equal footing, and he who ultimately passed judgment on the fates of both sons. Crown Prince Sun He and Prince of Lu Sun Ba were the two poles of the rivalry: the former held the heir's position yet lost favor; the latter harbored ambition and formed a faction. The court fractured accordingly: Chancellor Lu Xun, Gu Tan, Wu Can, Zhu Ju, and Zhuge Ke upheld the distinction between legitimate heir and other princes, standing with the crown prince; Bu Zhi, Quan Cong, and Lü Dai attached themselves to the Prince of Lu. The Quan Cong faction was especially active and served as the principal force in bringing false charges against the crown prince's partisans. Sun Quan's eldest daughter Sun Luban, who bore a grudge against Sun He's birth mother, Consort Wang, worked from within to spread slander — she was the key catalyst who inflamed the conflict. The old minister Gu Yong's faction (Gu Tan being his grandson) was swept up in the factional strife and exiled, demonstrating how broadly this struggle reached into the community of meritorious officials.
Core Issues
At its heart, the Struggle of the Two Palaces was not merely about which prince would succeed to the throne, but about how the relationship between the imperial authority of Eastern Wu and its community of meritorious officials was to be resolved. When Lu Xun and others repeatedly memorialized the throne calling for "a clear distinction between the legitimate heir and the other princes," they were ostensibly defending the heir's position, but in reality they were demanding that the sovereign abide by predictable rules of succession and restrain the arbitrariness of imperial power. Sun Quan was acutely wary of this: in his later years he was already apprehensive that the Jiangdong great-clan forces represented by Lu Xun had grown too powerful. The succession dispute happened to furnish a pretext, allowing him to use the factional struggle as cover for purging those senior officials who "interfered" in imperial family affairs and were deeply entangled with regional magnates. The struggle thus slid rapidly from a question of succession into a purge of meritorious officials by imperial authority.
Political Consequences
The outcome was a mutually destructive reckoning: Sun Quan deposed Crown Prince Sun He and exiled him to Nanyang, then ordered Prince of Lu Sun Ba to commit suicide and executed his partisans, and finally installed the young Sun Liang as crown prince. The senior officials who had supported the crown prince were either demoted or executed; Lu Xun, after repeated and severe reprimands, died of grief and indignation. The generation of meritorious officials and strategists who constituted Eastern Wu's most distinguished cadre was devastatingly weakened. Installing a child ruler then planted the seed of domination by powerful ministers — afterward Sun Jun and Sun Lin successively usurped control, palace coups occurred repeatedly, and Eastern Wu's central government remained chronically unstable. The Struggle of the Two Palaces can be said to mark the turning point at which Eastern Wu began its decline from strength, and Sun Quan's handling of it in his later years is widely regarded by later generations as the greatest political blunder of his life.
Counterfactual
Imagine that after Sun Deng's death, Sun Quan had only installed Sun He as crown prince while strictly suppressing the Prince of Lu's ritual rank and making the hierarchy unambiguous. The factional struggle might never have taken hold. Even if the brothers harbored animosity, it would have been difficult for courtiers to split into factions; Eastern Wu's community of meritorious officials would have remained intact, and the chain reaction of a child emperor succeeding and powerful ministers causing disorder might not have occurred. Yet the root of the problem may not have lain in the succession arrangement at all, but in Sun Quan's deep suspicion of the Jiangdong great clans in his later years. As long as that suspicion existed, he would eventually have found a pretext to purge the Lu Xun faction; the Struggle of the Two Palaces was simply the particular occasion he turned to his advantage. If so, the drain on Eastern Wu's vitality at the center was nearly unavoidable — the only difference would have been under what name, and in which year, it erupted.