According to old documents of Vietnam and China, in accordance with the common folk legends, Van Lang State of Hung Kings was followed by Au Lac State of An Duong Vuong. Au Lac was a historical fact and An Duong Vuong was a real historical figure.
However, about the history of Au Lac State with the central character An Duong Vuong Thuc Phan, so far, there are many problems to be solved, first of all the origin of Thuc Phan and the foundation of Au Lac State.
After the synthesis of research results, historians researching Co Loa analyzed and hypothesized that the residents of Van Lang under Hung Kings were mostly Lac Viet people and a part of Tay Au (also known as Au Viet) in the northern midland and mountains, living together in many areas. The north of Van Lang was the residence of Tay Au people (known as Au Viet); some groups of Lac Viet people coexisted. Many ancient historical books of China demonstrated that Lac Viet people were present both in Tay Giang basin, in the region of Quang Dong, Quang Tay, Hai Nam and a part of Van Nam, Quy Chau (Tran Quoc Vuong: The problem of Lac Viet people, Scientific – Historical Notice, University of Hanoi, Volume II, 1966, p.47 – 73.)
Lac Viet and Tay Au were two southern groups of Bach Viet, living close to each other and alternately, in the basin of Red River and Tay Giang River. Both were the same species, neighbors, Lac Viet and Tay Au people had close economic and cultural relations for long. Perhaps because of the alternative living situation and the close relationship, in some Chinese ancient documents, Tay Au and Lac Viet were distinguished, in other documents, they were considered to be one tribe.
Thuc Phan was the leader of a coalition of Tay Au tribes in the north of Van Lang; according to legend of the Tay ethnic group, the tribal coalition was “Nam Cuong State” consisting 10 tribes (9 tribes of 9 Lords and the center tribe of Thuc Phan) with the residence of the southern Quang Tay, Cao Bang and perhaps, the northern mountains and forests in North Vietnam, and the center was Cao Bang. Legend has it that An Duong Vuong Thuc Phan was “a mountainous chief”, a native in the forests and mountains in the north.
Between Lac Viet and Tay Au, as well as between Hung and Thuc, there was a long-standing close ties. Legend of Lac Long Quan – Au Co contained the relationship between two factors of Lac and Au in the ancient roots of the ethnic groups in Vietnam. Many legends about Hung Kings and An Duong Vuong considered Thuc Phan to be a part of the “seed”, “sects” or “grandchild” of Hung King. The legend saying that Thuc Phan was the “Lord of Ai Lao” also considered him as the head of a “bộ” (province) in 15 bộ of Van Lang, a “Hung Kings lineage” (Hung Kings jade annals) rather than a foreign stranger.
But on the other hand, at the end of Hung King’s reign, between Hung and Thuc protracted conflict occurred. Many villages in Red River Basin worshipping St. Tan Vien and generals of Hung Kings followed St. Tan Vien to “fight against Thuc aggressors”. That was an inevitable conflict in the process of collection of close tribes and tribal alliances to form the state and expand the scope of state control.
During the ongoing conflict, Van Lang State as well as Lac Viet and Tay Au people and the entire groups in blocks of Bach Viet faced a threat. That was the large-scale invasion of the Qin Empire. This historical circumstance explained the reason why the conflict between Hung and Thuc ended by Hung King ceding the throne to Thuc Phan and the foundation of Au Lac was a successor development of Van Lang, an integration at a higher level and wider range of Lac Viet and Tay Au people.