During the reign of Emperor Hui of Jin, Sima Zhong, the state had already fallen into chaos. To contend for the throne, several princes of the Sima clan fought fiercely among themselves, using Emperor Hui as a pawn in their power struggles, and he was eventually poisoned to death by one of them. In fact, more than eight princes participated in the struggle for central authority, but the others had less impact than these eight in the melee, which is why this conflict is known as the War of the Eight Princes. The eight princes were Sima Liang, the Prince of Runan; Sima Wei, the Prince of Chu; Sima Lun, the Prince of Zhao; Sima Jiong, the Prince of Qi; Sima Yong, the Prince of Hejian; Sima Ying, the Prince of Chengdu; Sima Yi, the Prince of Changsha; and Sima Yue, the Prince of Donghai.
After ascending the throne, Emperor Wu of Jin, to prevent the state from being seized by outsiders, enfeoffed many princes within the Sima clan, granting them not only the authority to govern their territories but also the power to command local armies and mobilize troops independently. In this way, the entire state remained under the control of the Sima family. However, Emperor Wu failed to anticipate that while this policy prevented outsiders from dominating the court, it would also place his own descendants in peril, greatly increasing the chances of usurpation by members of his own clan.
Before his death, Emperor Wu of Jin issued an edict entrusting Sima Liang, the Prince of Runan, and Yang Jun, the father of the empress, with jointly assisting Emperor Hui of Jin. However, Yang Jun wanted to seize power alone, so he requested that Emperor Wu revise the edict, removing Sima Liang's name from the list of regents. Emperor Wu, already on his deathbed, had no choice but to comply with Yang Jun's wishes and summoned officials to draft a new edict.
Not long after, Emperor Wu of Jin passed away, and Yang Jun began to serve as regent. Sima Liang, knowing that Yang Jun would not let him off, simply fled to Xuchang to hide. Yang Jun thought that no one could threaten his position anymore and felt quite pleased with himself, but within a few days, he realized things were not that simple.
Empress Jia Nanfeng of Emperor Hui of Jin was short, dark, and ugly, with a violent and brutal personality. Seeing that all court power was firmly in the hands of Yang Jun, she grew deeply discontented. Ever since Sima Zhong became Emperor Hui of Jin, Jia Nanfeng had been plotting daily how to use the emperor to control the government. With such ambitions, she naturally could not tolerate Yang Jun's arrogant demeanor. Knowing she could not openly confront Yang Jun, she pondered repeatedly and decided to win over the Prince of Runan, Sima Liang, and the Prince of Chu, Sima Wei. Jia Nanfeng ordered Sima Wei to mobilize all the troops from Jingzhou to Luoyang, secretly securing key exit routes from the city. When Yang Jun heard of Sima Wei's troop movements, though frightened, he dared not intervene to stop them.
In 291 AD, Empress Jia, using Emperor Hui's name, issued an edict dismissing Yang Jun from his official post, accusing him of plotting rebellion. Prince Sima Wei of Chu then stationed his troops at the imperial palace and surrounded Yang's residence. Yang Jun and his entire family were killed, and his clan was exterminated to the third degree of kinship. After Yang Jun's death, Prince Sima Liang of Runan and the minister Wei Guan became the new regents. Empress Jia was dissatisfied with this outcome, as she did not hold all the power herself. Prince Sima Wei of Chu had control over part of the imperial guard in the capital. Worried that Sima Wei might also seek to usurp power, Sima Liang and Wei Guan planned to strip him of his military command and send him back to his fiefdom.
Sima Wei harbored resentment and sought revenge against Sima Liang and Wei Guan, so he aligned himself with Empress Jia. Jia Nanfeng, who was worried about finding allies to expand her power, immediately appointed Sima Wei as Grand Tutor to the Crown Prince, allowing him to remain in Luoyang. Subsequently, the empress, using Emperor Hui's name, issued an edict declaring that Sima Liang and Wei Guan were plotting rebellion and ordered Sima Wei to lead troops to surround their homes, where both Sima Liang and Wei Guan were killed by soldiers.
Empress Jia feared that Sima Wei knew too many inside secrets and would one day threaten her, so after Sima Wei killed Sima Liang and Wei Guan, she issued an imperial edict in Emperor Hui's name, accusing Sima Wei of fabricating the rebellion of the Prince of Runan and Wei Guan, and of forging the emperor's decree, ordering his arrest. Sima Wei did not expect Empress Jia to frame him; knowing he could not escape death, he did not flee and allowed Empress Jia's men to bind him and take him to prison. Within a few days, Sima Wei was executed. His friend Qi Sheng, who had advised him to expand his power after the deaths of Sima Liang and Wei Guan, was also put to death when Empress Jia later learned of this.
After this, Empress Jia's power reached its peak, with her confidants occupying every official position in the court. To fully control the government, Empress Jia began to frame Crown Prince Sima Yu. Since Sima Yu was not Empress Jia's biological son but was born to Consort Xie, Jia Nanfeng feared that after Sima Yu ascended the throne, he would depose her as empress dowager, so she planned to first remove him from his position as crown prince. At that time, the crown prince's tutor was Sima Lun, the Prince of Zhao, who, along with the official Sun Xiu, learned of Empress Jia's scheme. Initially, they intended to prevent the crown prince's death, but Sun Xiu realized that even if the crown prince were saved, he might not reward them after taking the throne. So he advised Sima Lun to let Empress Jia proceed with framing Crown Prince Sima Yu. Not only that, but Sima Lun and Sun Xiu also urged Jia Nanfeng to execute the crown prince quickly to eliminate future trouble. Soon after, Crown Prince Sima Yu was killed in the Jinyong City where he was under house arrest. When the news reached Luoyang, Sima Lun and Sun Xiu, in collusion with other officials, forged an edict from Emperor Hui ordering the arrest of Empress Jia and her confidants. Subsequently, Sima Lun forged another edict appointing himself as prime minister, while Sun Xiu and others received many rewards and titles.
In 301 AD, Sima Lun deposed Emperor Hui of Jin and proclaimed himself emperor, but his poor governance and moral corruption led to political turmoil and deceit among officials. The princes Sima Yong of Hejian, Sima Ying of Chengdu, and Sima Jiong of Qi, unwilling to be ruled by a fellow feudal lord, united to launch a rebellion.
The three princes led their respective armies to converge at Luoyang, where they fought against Sima Lun's forces for over two months. Despite heavy casualties, they ultimately killed Sima Lun and eliminated many of his followers. Subsequently, Sima Jiong reinstated Emperor Hui of Jin, Sima Zhong, to the throne, while appointing himself as Grand Marshal and granting high-ranking titles and generous rewards to Sima Yong and Sima Ying. However, this peace was short-lived; after seizing power, Sima Jiong indulged in a life of debauchery, plunging the imperial court back into chaos and creating opportunities for other feudal princes to seize power.
Prince Sima Yong of Hejian, instigated by the imperial guard commander Li Han, raised an army to attack Sima Jiong in an attempt to usurp power, even listing many of Sima Jiong's alleged crimes to portray himself as acting on Heaven's behalf. Not only that, but Sima Yong also falsely claimed that Prince Sima Ai of Changsha was part of his own camp, hoping to use Sima Jiong's hand to eliminate Sima Ai, then focus solely on dealing with Sima Jiong. Unexpectedly, Sima Ai thoroughly defeated Sima Jiong, achieving an unforeseen victory. Sima Yong was stunned; seeing the regime fall into Sima Ai's hands, he was furious but had no way to vent his anger.
In 303 AD, Sima Yong allied with Sima Ying, the Prince of Chengdu, and raised an army of 270,000 to attack Luoyang. Emperor Hui of Jin appointed Sima Yi as Grand Commander to lead the defense. After several months of fighting, Sima Yi ultimately emerged victorious. However, Sima Yue, the Prince of Donghai, took advantage of Sima Yi's absence from the capital to secretly bribe several imperial guard commanders, who then seized Sima Yi and imprisoned him in Jinyong City under house arrest. Emperor Hui subsequently appointed Sima Yue as Minister of Works. Later, Sima Yue, in league with Zhang Fang, a subordinate of Sima Yong, had Sima Yi burned to death and executed many of his followers.
During the power struggles among the feudal princes, Emperor Hui of Jin was merely a political tool, holding the title of emperor in name only. Sima Ying forced him to appoint himself as Prime Minister and Sima Yong as Grand Chancellor, and also issued an edict deposing the crown prince, Sima Tan. Believing he had secured power, Sima Ying gradually disregarded Emperor Hui, indulging in pleasure and leisure. However, not long after, Sima Yue, the Prince of Donghai, gathered over a hundred thousand troops to attack Sima Ying. After a chaotic battle, Sima Yue was defeated and fled to Xiapi. Upon hearing the news, Sima Yong sent troops to reinforce Sima Ying, seized the opportunity to storm the imperial palace, and took control of Emperor Hui.
In 305 AD, Sima Teng, the younger brother of Sima Yue, assembled an army to avenge his brother, and Sima Ying immediately sent troops to suppress him but was defeated by Sima Teng and fled to Chang'an. Sima Yong then forced Emperor Hui of Jin to issue an edict summoning Sima Yue back to the capital to co-govern, but Sima Yue refused. In truth, Sima Yue wanted to seize power for himself, and soon after rejecting Sima Yong's invitation, he launched a military campaign against Luoyang. Along the way, Sima Yue won over many local officials, and the Prince of Dongping, Sima Mao, also submitted to him. Upon learning of Sima Yue's advance, Sima Yong panicked and forced Emperor Hui to issue an edict stripping Sima Yue of his noble title, but Sima Yue openly broke ties, raised the banner of rebellion, and marched on Luoyang with great fanfare.
After a year of chaotic warfare, Sima Yue defeated Sima Yong and emerged victorious in the struggle for political power. Subsequently, Sima Yue poisoned Emperor Hui of Jin, installed Sima Chi as Emperor Huai of Jin, and completely took control of the imperial court.
The War of the Eight Princes severely weakened the Jin Dynasty's authority, causing a dramatic decline in the central power of the Central Plains, leading to frequent invasions by foreign tribes, plunging the common people into extreme suffering as their peaceful lives were shattered by relentless warfare.