Gongsun Yuan's repeated communication with and sales of horses to Eastern Wu angers Cao Rui, who in 232 orders his generals Tian Yu and Wang Xiong to attack Liaodong against the advice of Jiang Ji; the attacks are unsuccessful, although Tian is able to intercept the Eastern Wu horse-buying fleet and destroy it.

After the incident, although Gongsun formally maintains vassalage to Cao Wei, the relationship is damaged.

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.

Gongsun, apprehensive of another attack from Cao Wei, sends ambassadors to Eastern Wu in 233 to formally submit to its emperor, Sun Quan.

Sun is so pleased that he immediately creates Gongsun the Prince of Yan and grants him the nine bestowments, which are typically reserved for officials so powerful that the bestowments were typically viewed as a sign that the emperor was about to abdicate to them.

However, Gongsun realizes later that Eastern Wu will be of little help in an expedition against him.

He betrays Eastern Wu, slaughters Sun's ambassadors as they arrive in Liaodong, and seizes their troops.

In response, Cao Rui creates Gongsun the Duke of Lelang.

(Part of the Eastern Wu troops are able to escape and eventually return home with the assistance of Goguryeo, a rival of the Gongsuns.)

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.

Another serious crisis posed by Eastern Wu occurs in 234, when Eastern Wu, in a semi-coordinated effort with Shu Han, launches an attack against Cao Wei simultaneously with Zhuge Liang's Northern Expeditions.

At the time, many frontline officials are on family leave, so Man Zhong requests Cao Rui to call them back to fight Sun Quan.

Cao Rui refuses to cancel his subordinates' vacations, and orders Man to focus on the defense.

Cao Rui then personally leads the royal army as reinforcement, and acts as an effective coordinator of the various forces that Cao Wei has on Eastern Wu's borders, and Eastern Wu is unable to make substantial gains.

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.

Cao Rui, angered in 237 by reports that Gongsun has repeatedly defamed him, once again considers attacking Liaodong.

He commissions Guanqiu Jian to prepare for an attack, then orders Gongsun to come to Luoyang for an official visit.

Gongsun refuses and instead declares independence.

Guanqiu attacks him, but is stopped by torrential rains.

Gongsun then declares himself the Prince of Yan and enters into alliances with the Xianbei tribes to harass Cao Wei's borders.

Cao Rui sends Sima Yi with forty thousand men to attack Liaodong the following year.

Upon hearing this, Gongsun again requests aid from Eastern Wu.

Sun, angry at Gongsun's previous betrayal, pretends to agree, but does not send Gongsun any actual help.

Although Sima's expeditionary force is also initially halted by torrential rains as had been that of Guanqiu, Sima waits out the rains and eventually surrounds Gongsun's capital of Xiangping (in modern Liaoyang, Liaoning), starving Gongsun's troops.

Xiangping falls after nearly three months of siege; Gongsun flees, but is captured and executed by Sima.

Liaodong becomes part of Cao Wei's domain.

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.