Collapse and Revival of Balhae
Chinese scholars claim that after Balhae fell to the Liao dynasty (Khitan Empire), most refugees migrated to Liao, and those who entered Goryeo were very small in number. Balhae is claimed to be a part of Chinese history, because Balhae fell to the Liao dynasty and Khitan's Liao dynasty was absorbed into modern-day China.
Although Inseon Dae, the last king of Balhae, surrendered to the Liao dynasty, the people of Balhae rejected their rule and continued to conduct revival movements. According to historical records, revival efforts by the Balhae refugees continued for decades and include Later Balhae, Jeong-an Kingdom, Heungyo Kingdom, and Greater Balhae. This proves that the Balhae refugees fiercely contested Liao dynasty rule.
The fact that Gwang-hyeon Dae, the last Crown Prince of Balhae, led tens of thousands of his people to Goryeo is a testament to how the people of Balhae perceived Goryeo. According to the History of Goryeo, the migration of Balhae refugees to Goryeo continued until the 11th year of Yejong, Goryeo period (1116). A collective migration of tens of thousands of people continued for generations.
Goryeo's treatment of Balhae refugees clearly indicates the successive relationship between Balhae and Goryeo. After the fall of Balhae, Taejo of Goryeo (Wang Geon) referred to Balhae as a kingdom of relatives. He granted Gwang-hyeon Dae the surname Wang (King) and allowed him to conduct commemorative rites for his ancestors. When the Liao dynasty sent delegates to Goryeo, Taejo refused their company on the basis that Liao was responsible for the collapse of Balhae. The infamous Manbu Bridge Incident occurred around this time.
Manbu Bridge Incident
When the Emperor Taizong of Liao sent delegates to Goryeo in the 25th year of Taejo (942), Wang Geon banished the 30-member envoy to an island and ordered the 50 camels brought as gifts to be tied under a bridge to die of starvation.