Nguyen Phuc Anh (1761-1820) was the strongest of Nguyen leaders who faced the Tay Son and other rivals for many years. He was also the first to turn to the French for help against his rivals. This was before he became the first Nguyen emperor of Vietnam and the founder of the Nguyen Dynasty (1802-1945).
He actually permitted a French missionary, Pierre Pigneau de Béhaine, to intercede in 1787 to seek French aid against his rivals.
The original treaty-based relationship of 1787 between Vietnam and France promised missionary and commercial rights to France and military aid to Nguyen Anh. France was also promised the city of Da Nang (which later under the French became Tourane) and the island of Con Son. The terms of the 1787 treaty were not to be realized, however, until much later (1862).
Nguyen Anh, therefore, accomplished his goals without French assistance. He declared himself Emperor Gia Long. His newly acquired name reflected the joining of Gia Dinh (then the name used for Saigon) and Long (part of the old name for Hanoi, Thang Long). Thus, he as emperor represented a unification of Vietnam not known for centuries.
To confirm his power and to symbolize his dynasty, he moved the capital from Hanoi to Hue and he changed the name of the state to Vietnam.
Nevertheless, Gia Long obtained recognition of his newly established power by seeking the endorsement of China and by adopting Chinese as Vietnam's official written language. This meant an end to use of nom.
Up until his death in 1820, when his son succeeded as Emperor Minh Mang, Gia Long tolerated French missionaries but disapproved further French economic developments in Vietnam.
University of Richmond