Sun Deng

Sun Quan’s eldest son, Sun Deng, perhaps concerned about the apparent deterioration in the emperor’s judgment, leaves the western empire in Lu Xun's hands in 232 and returns to Jianye, where he will remain until his own death in 241.

In 232, Sun Quan has another misadventure involving his navy—as he sends his generals Zhou He and Pei Qian to the nominal Wei vassal Gongsun Yuan, in control of Liaodong prefecture (present-day central Liaoning), to purchase horses, against the advice of Yu Fan—and indeed, he exiles Yu Fan to the desolate Cangwu prefecture (roughly modern Wuzhou, Guangxi) as punishment.

Just as Yu Fan had predicted, however, the venture ends in failure—as Zhou He and Pei Qian, on their return, are intercepted by Wei forces and killed.

Regretting his actions, Sun Quan tries to recall Yu Fan back to Jianye, only to learn that Yu has died in exile.

Sun Quan has yet another misadventure in his dealings with Gongsun Yuan in 233, Gongsun sends messengers to him, offering to be his subject.

Sun Quan, ecstatic, appoints Gongsun Yuan the Prince of Yan, grants him the nine bestowments, and further sends a detachment of ten thousand men by sea north to assist Gongsun Yuan in his campaign against Wei, against the advice of nearly every single one of his high level officials, particularly Zhang Zhao.

Once the army arrives, however, Gongsun Yuan betrays them, killing Sun Quan's officials Zhang Mi and Xu Yan), whom Sun had sent to grant the bestowments and seizes their troops.

Once this happens, the enraged Sun Quan wants to personally head north with a fleet to attack Gongsun Yuan, and initially, not even Lu Xun's opposition is able to dissuade him, although he eventually calms down and does not follow through.

To his credit, he also personally goes to Zhang Zhao's house and apologizes to him.

Sun Quan, in coordination with Zhuge Liang's final northern expedition against Wei, personally leads a major attack against Wei's border city Hefei in 234, while having Lu Xun and Zhuge Jin attack Xiangyang, with the strategy of trying to attract Wei relief forces and then attacking them.

However, Wei generals correctly see the situation and simply let Sun Quan besiege Hefei.

Only after Sun Quan's food supplies run low does Cao Rui personally arrive with reinforcements, and Sun withdraws, as do Lu Xun and Zhuge Jin.

Sun Quan is still capable of making proper decisions at times, despite the deterioration in his previous clear thinking.

For example, when, as a sign of contempt, Wei's emperor Cao Rui offers him horses in exchange for pearls, jade, and tortoise shells in 235, Sun Quan ignores the implicit insult and makes the exchange, reasoning that his empire needs horses much more than pearls, jade, or tortoise shells.

Gongsun Yuan is under attack by Wei's general Sima Yi in 238.

Sun Quan, despite his prior rage against Gongsun, correctly judges the situation as one where he might be able to take advantage if Sima Yi were initially unsuccessful, and does not immediately refuse Gongsun's request for help.

However, as Sima Yi is able to conquer Gongsun Yuan quickly, Sun Quan never launches the major attack that he had considered were Sima to have gotten stuck in a stalemate with Gongsun.

In this year, he also recognizes the manner in which his head secretary Lü Yi had been falsely accusing his officials, and has Lü executed; he then further confirms his trust in the high level officials by personally writing an emotional letter to Zhuge Jin, Bu Zhi, Zhu Ran, and Lü Dai, blaming himself for the recent problems with his administration while urging them to speak out honestly whenever they see faults in him.

Sun Quan appoints his son Sun He, born to Consort Wang, crown prince in 242.

However, he also favors another son by Consort Wang, Sun Ba, the Prince of Lu, and permits Sun Ba to have the same staffing level as the crown prince—a move to which a number of officials object, as encouraging Sun Ba to compete with Sun He, but Sun Quan does not listen to them.

Sun Quan launches the last major assault of his reign against Wei in 241, in light of Cao Rui's death in 239, but he rejects a strategy offered by Yin Zha to attack Wei in a coordinated effort with Shu on four different fronts, and the campaign ends in failure.

The death of the crown prince Sun Deng later in 241 leaves open the issue of succession and appears to mark the start of a precipitous decline in Sun Quan's mental health.