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Vietnam via the Bach Dang estuary (mouth of the river which flows into Halong Bay) where iron-tipped stakes had been sunk into the riverbed by Ngo Quyen. At high-tide a Vietnamese flotilla attacked the enemy then, pretending to escape, lured the Southern Han boats into the estuary beyond the stakes still covered by the tide. At low-tide, the entire Vietnamese fleet counter-attacked, forcing the enemy to flee and sink, impaled on the barrage of stakes.
 

Ngo Quyen imperial tomb

The Bach Dang victory in 938 put an end to the period of Chinese imperial domination. In 939 Ngo Quyen proclaimed himself king, established his capital at Co Loa (previously a capital in the 3rd century B.C.) and set up a centralized government. It was the first truly independent Vietnamese state.

Domestically, the main obstacle to the founding of a centralized power structure capable of assuming direction of the economy - management of the dyke system in particular - and of successfully resisting foreign aggression was the existence of feudal lords who each ruled an area of territory. On the death of Ngo Quyen in 944, 12 warlords divided the country among themselves and began to fight one another.

Source: VNAT