In 280 AD, the Western Jin dynasty finally unified China by conquering the state of Wu. Emperor Sima Yan initially ruled with wisdom, but after unification, he fell into laziness and luxury, failing to properly establish a succession plan or manage the growing power of relocated nomadic tribes.
After Sima Yan's death, his son Emperor Hui (Sima Zhong) ascended the throne, but his severe intellectual disabilities made him unable to govern effectively. This created a power vacuum that was exploited by his ambitious wife, Empress Jia Nanfeng. Her ruthless manipulation triggered a brutal 16-year civil war known as the 'War of the Eight Princes,' which devastated the economy and annihilated the central government's military strength.
During this chaos, nomadic tribal leaders in northern China, who had been recruited as mercenaries or forced to settle inside the empire, saw an opportunity to declare independence. Liu Yuan, a Xiongnu leader, declared himself the heir to the Han dynasty and established the state of Han Zhao.
The weakened Jin could not withstand the onslaught. In 311 AD, the capital Luoyang was captured and looted by nomadic forces, and Emperor Hui was taken prisoner, an event known as the Disaster of Yongjia. Five years later, the last major stronghold, Chang'an, fell, marking the complete end of the Western Jin dynasty.
The surviving imperial family members and their supporters fled south across the Yangtze River and established the Eastern Jin dynasty with Jiankang (modern-day Nanjing) as its capital. Meanwhile, the nomadic tribes that occupied Northern China began establishing their own states, marking the beginning of the chaotic Sixteen Kingdoms period.