Since 905, Tĩnh Hải circuit had been ruled by local Vietnamese governors like an autonomous state. Tĩnh Hải circuit had to paid tributes for Later Liang dynasty to exchange political protection. In 923, the nearby Southern Han invaded Jinghai but was repelled by Vietnamese leader Dương Đình Nghệ. In 938, the Chinese state Southern Han once again sent a fleet to subdue the Vietnamese. General Ngô Quyền (r. 939–944), Dương Đình Nghệ's son-in-law, defeated the Southern Han fleet at the Battle of Bạch Đằng (938). He then proclaimed himself King Ngô, established a monarchy government in Cổ Loa and effectively began the age of independence for Vietnam.