When northern China fell into chaos, Cai Mo migrated to the south, where he became a prominent minister during the early Eastern Jin period.
He was most notable for his work as the Minister of Ceremonies and for being a vocal opponent of his state's attempts at reclaiming the north from their rival, Later Zhao.
Cai Mo came from a line of officials in Kaocheng County (考城縣), Chenliu Commandery (陳留郡), in present-day Kaifeng, Henan.
[3] Cai Mo eventually decided to move south of the Yangtze to avoid the turmoil and serve the Prince of Langya and Inspector of Yangzhou, Sima Rui.
However, Cai Mo later joined Wen Jiao's loyalist coalition against Su Jun and gave Yu Bing his position back.
Cai Mo attempted to resign and suggested that Kong Yu and Zhuge Hui receive his rewards, but the court refused.
Cai Mo was demoted to a commoner when, while supervising the ancestral temple, the person in charge forgot to set up the memorial tablet for Emperor Ming of Jin.
Cai Mo asserted that the emperor should be allowed to order music performed in the ancestral temple when sending envoys, and the court should obey this decision.
[8] In another incident, the Prince of Pengcheng, Sima Hong (司馬紘), informed the court of the portraits of Buddha in Lexian Hall (樂賢堂).
While Cai Mo acknowledged that the paintings might have been blessed and protected the hall, he pointed out that the rebellion destroyed the rest of Jiankang, so it would be inappropriate for the court to extol them.
He also brought up the past failings of Zu Ti's northern expeditions and the difficulties of crossing the rivers dividing Jin and Zhao.
When Yu Liang attempted his expedition later that year following Prime Minister Wang Dao's death, he was soundly defeated by Zhao, just as Cai Mo expected.
[12] Shortly after Xi Jian's death, another commander, Chen Guang (陳光), wanted to campaign against Later Zhao, so the court sent him to attack Shouyang.
He said that Shouyang's defences were too strong, that the Zhao army would be quick enough to respond to any intrusion, and that it would be wasteful to use the state's elite soldiers to take an area that would bring little benefit.
The issue troubled the court, which prompted Cai Mo to have the general, Xu Xuan (徐玄) and others guard the Central Plains.
The general, Yin Hao, whom the court had appointed to command the military expeditions, initially pushed for Cai Mo's execution.
However, Yin Hao's friend, Xun Xian, successfully changed his mind, fearing Cai Mo's potential to rebel.
[19] Years after his removal, the Empress Dowager offered him to return to the government as Household Counsellor with the privilege of a Separate Office with equal ceremonial to the Three Excellencies.