Emperor Mu of Jin (simplified Chinese: 晋穆帝; traditional Chinese: 晉穆帝; pinyin: Jìn Mù Dì; Wade–Giles: Chin Mu-ti; 343 – July 10, 361[1]), personal name Sima Dan (司馬聃), courtesy name Pengzi (彭子), was an emperor of the Eastern Jin Dynasty.
In 345, after Yu Yi, who had served as the commander of military forces in the western provinces (roughly covering modern Hubei, Hunan, Guizhou, and Yunnan), died, the ambitious general Huan Wen (an uncle of Emperor Mu by marriage, having married his aunt Sima Xingnan (司馬興男) the Princess Nankang) was put in charge of those provinces.
In late 346, Huan, despite a lack of approval from the central government, started a campaign to conquer Cheng-Han, a rival state that possessed modern Sichuan and Chongqing.
In 349, with rival Later Zhao in a state of disarray following the death of its emperor Shi Hu and the subsequent internecine warfare between his sons and his adopted grandson Shi Min, many of Later Zhao's southern provinces switched their allegiance to Jin, and Huan prepared a northern excursion.
Instead, the imperial government, under Sima Yu and Yin, sent Emperor Mu's grandfather Chu Pou.
Chu, however, withdrew after some initial failures, and the campaign resulted in the death of many civilians who were intending to defect to Jin.
Yin was shocked, and initially considered either resigning or send the imperial banner of peace (Zouyu Fan, 騶虞幡) to order Huan to stop.
In spring 357, as Emperor Mu had his rite of passage (at age 13), Empress Dowager Chu terminated her own regency, and from that point on, Emperor Mu became officially the decision maker, although effectively, Sima Yu and Huan Wen continued to make the decisions.
Later that year, a northern campaign by the general Xun Xian, intending to recapture the Shandong Peninsula, failed.
Empress Dowager Chu therefore ordered that his cousin, Sima Pi the Prince of Langya, be made emperor.