War of the Eight Princes

Sima Yan (Emperor Wu), the founder of the Jin, had given his uncles, cousins and sons princedoms with their own armies, hoping that they would protect the dynasty and his heir. That heir, Sima Zhong, who reigned as Emperor Hui from 290, was developmentally disabled, and whoever controlled him controlled the government. On the night of 23 April 291 Empress Jia Nanfeng, with the help of Sima Wei, Prince of Chu, overthrew and killed the regent Yang Jun (Sima Liang, whom she had also approached, held back and became regent after the coup); three months later, at the empress’s instigation and armed with an edict, Sima Wei killed Sima Liang, after which the empress had him executed for the killing. The empress then ruled for nine years, until in 300 Sima Lun, Prince of Zhao, deposed her and forced her to take poison; in February 301 he took the throne himself.

The usurpation turned intrigue into war. Sima Jiong, Sima Ying and Sima Yong — the “Three Princes” — raised armies, Sima Lun was forced to take his own life and Emperor Hui was restored, but the victors soon turned on one another. Sima Ai killed Sima Jiong in January 303, held Luoyang through a long siege and in 304 was handed over to his enemies and burned alive; Sima Ying and Sima Yong in turn took possession of the emperor, who was wounded and captured in battle in 304 and carried to Ye and then to Chang’an. The princes brought in Xianbei and Wuhuan cavalry, who sacked Ye in 304 and Chang’an in 306. In 306 Sima Yue, Prince of Donghai, prevailed: on 28 June he brought Emperor Hui back to Luoyang, Sima Ying and Sima Yong were killed that winter, and in January 307 the emperor died, probably poisoned.

The war was a struggle for the person of the emperor rather than a single campaign — the name comes from the joint biography of eight princes in chapter 59 of the Book of Jin, compiled in the 7th century, and the eight never all fought on one side — but it devastated the Jin heartland. While the princes fought, in 304 Liu Yuan, a noble of the Southern Xiongnu serving Sima Ying, was proclaimed their chanyu and then King of Han, and Li Xiong founded the Cheng-Han state in Sichuan: the Sixteen Kingdoms period had begun. Historians date the war 291–306; the last rival princes died in the winter of 306–307, still within the Chinese year that corresponds to 306.