Nguyễn Ánh, whose family, the Nguyễn family, had been decimated by the Tây Sơn rebellion when he was 16 or 17, received the protection and aid of the French Catholic priest Pigneau de Béhaine, titular bishop of Adran.

[3] That treaty marks the beginning of French influence in Indochina, but the Governor of Pondicherry, Count de Conway, who was given authority to decide on the actual implementation of the treaty, refused to follow through with it, leaving Pigneau de Béhaine to his own means.

In spite of these inconveniences, between 1789 and 1799 a French force mustered by Pigneau de Béhaine managed to support Gia Long in acquiring sway over the whole of Vietnam.

[5] The French trained Vietnamese troops, established a navy, and built fortifications in the Vauban style,[3] such as the Citadel of Saigon.

Several of these French adventurers would remain in high positions in the government of Gia Long such as Philippe Vannier, Jean-Baptiste Chaigneau, de Forçant and the doctor Jean Marie Despiau.