The Disaster of Yongjia (simplified Chinese: 永嘉之乱; traditional Chinese: 永嘉之亂) refers to events in Chinese history that occurred in 311 CE, when Han Zhao forces, mostly from Xiongnu and other non-Han ethnic groups, captured and sacked Luoyang, the capital of the Jin dynasty. After this victory, Han Zhao's army committed a massacre when entering the city, killing the Jin crown prince, a host of ministers, and over 30,000  civilians. They also burnt down the palaces and dug up Jin mausoleums. This was seen as the event that led to the fall of the unified Western Jin dynasty and its re-establishment as the Eastern Jin dynasty, as well as the loss of northern China to a series of short-lived dynasties known as the Sixteen Kingdoms.
The Disaster of Yongjia was also a major impetus for the mass migration expansion of Han Chinese people into modern southern China. Many clan genealogies ascribe this event in particular as the reason why their ancestors moved from the north to places in Fujian and Guangdong etc.