After Overthrowing Sima Lun
Some thought that a power balance that Emperor Wu had hoped for at his death might be restored, as Princes Jiong and Ying were each given regent titles (and awarded the nine bestowments, in one rare case where the nine bestowments were not signs of an impending usurpation, although Prince Ying declined the bestowments), and many talented officials were promoted into important positions. However, the Princes Jiong and Ying were actually apprehensive of each other's power, and Prince Ying decided to yield the central government regency to Prince Jiong at the time and return to his defense post at Yecheng. When he bid farewell to Sima Jiong, he did not talk about politics at all but only about his mother's illness, and this brought further praise on his character, as did his subsequent acts to collect the bodies of soldiers who died in the war against Sima Lun to give them proper burials.
In the capital, Sima Jiong became arrogant based on his accomplishments. He had his sons created princes, and ran the matters of the central government from his mansion, rarely visiting the emperor or attending the imperial meetings. He enlarged his mansion to be as large as the palace, and he entrusted matters to people who were close to him, and would not change his ways even when some of his more honest associates tried to change his behavior. When Emperor Hui's grandsons Sima Zang and Sima Shang (司馬尚), successive crown princes, died in childhood, leaving Emperor Hui without male descendants by 302, Sima Ying was considered the appropriate successor, but Sima Jiong chose to bypass him by recommending the seven-year-old Sima Qin (司馬覃) the Prince of Qinghe (Emperor Hui's nephew and the son of his brother Sima Xia (司馬遐)) as the crown prince, with intent to easily control the young Crown Prince Qin.
Sima Jiong became suspicious of Sima Yong the Prince of Hejian—because Sima Yong had initially wanted to support Sima Lun, until he saw that Sima Lun's cause was hopeless. Sima Yong knew of Sima Jiong's suspicion, and started a conspiracy; he invited Sima Ai the Prince of Changsha to overthrow Sima Jiong, believing that Sima Ai would fail; his plan was then to, in conjunction with Sima Ying, start a war against Sima Jiong. Once they were victorious, he would depose Emperor Hui and make Sima Ying the emperor, and then serve as Sima Ying's prime minister. In winter 302, Sima Yong declared his rebellion, and Sima Ying soon joined, despite opposition from his strategist Lu Zhi (盧志). Hearing that Sima Ai was part of the conspiracy as well, Sima Jiong made a preemptive strike against Sima Ai, but Sima Ai was prepared and entered the palace to control Emperor Hui. After a street battle, Sima Jiong's forces collapsed, and he was executed. Sima Ai became the effective regent, but in order to reduce opposition, he submitted all important matters to Sima Ying, still stationed at Yecheng.
After Sima Jiong's death, Sima Ying became extremely arrogant as well, and trusted inappropriate persons, chief among whom was his servant Meng Jiu (孟玖). Even though Sima Ai submitted all important matters to him, he still considered Sima Ai an interference to his control of government and wanted to eliminate him. At the same time, Sima Yong, who had hoped that if Sima Ying became emperor he could then be prime minister, persuaded Sima Ying to again join him against Sima Ai. They started military action against Sima Ai in fall of 303, and while they had overwhelming force, their forces could not score a conclusive victory against Sima Ai. Sima Yong's forces were about to withdraw in spring 304 when Sima Yue the Prince of Donghai, the grandson of a great-granduncle of Emperor Hui, believing that Sima Ai could not win this war, arrested him and delivered him to Sima Yong's general Zhang Fang (張方), who executed Sima Ai cruelly by burning him to death. Sima Ying became in effective control of the government, but continued to control it remotely from Yecheng.
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