The Rise and Fall of the Kingdom of Balhae
In 690, Wu Zetian (Empress of the Gaozong Emperor of Tang Dynasty) proclaimed herself Empire, and changed the dynasty name from Tang to Zhou (690–705). Six years later, the Khitan people of the Yingzhou region declared a rebellion against Wu Zetian’s rule. The Sumo people, under the leadership of Sumo leader Dae Jung- sang and Baishan leader Geolsa Biu, took this opportunity to cross the Liao River, and return to their homeland.
To prevent the royal court from being caught between the hammer and the anvil, rulers of the Zhou Dynasty forcefully repressed the Khitans, while also showing geniality toward the Mohe people, pardoning the punishments for their treasons of traveling east without permission, and granting royal titles to Dae Jung- sang and Geolsa Biu. However, the two leaders refused the pardons, and continued their revolt on the Zhou Dynasty.
After her attempts at peace had proven fruitless, Wu Zetian sent General Li Kaigu to crusade against the Mohe people. Geolsa Biu died in battle, and Dae Jung-sang suffered the same fate while escaping, after which the people of both tribes scattered and fled. Fortunately, Dae Jung- sang had a son, named Dae Jo-yeong, who proved to be a skilled strategist; he led the remaining soldiers to defeat the Zhou forces, then seized the chance to gather the remnants of Geolsa Biu and a portion of the Goguryeo people, capturing a key location on the upper reaches of the Mudan River.
In 698, Dae Jo-yeong established the Kingdom of Zhen, which at the time had a population of less than 700,000, by no means a large host, but the Zhou