French assistance to Nguyễn Ánh

French assistance to Nguyễn Phúc Ánh (commonly known by his era name as the Gia Long Emperor), the future founding emperor of the Nguyễn dynasty, covered a period from 1777 to 1820. From 1777, Mgr Pigneau de Behaine, of the Paris Foreign Missions Society, had taken to protecting the young Vietnamese prince who was fleeing from the offensive of the Tây Sơn. Pigneau de Behaine went to France to obtain military aid, and secured a France-Vietnam alliance that was signed through the 1787 Treaty of Versailles between the king of France, Louis XVI, and Prince Nguyễn Phúc Ánh. As the French regime was under considerable strain at the eve of the French Revolution, France was unable to follow through with the application of the treaty. However, Mgr Pigneau de Behaine persisted in his efforts and, with the support of French individuals and traders, mounted a force of French soldiers and officers that would contribute to the modernization of the armies of Nguyễn Ánh, making possible his victory and his reconquest of all of Vietnam by 1802. A few French officers would remain in Vietnam after the victory, becoming prominent mandarins. The last of them left in 1824 following the enthronement of Minh Mạng, Gia Long's successor. The terms of the 1787 Treaty of Alliance would still remain one of the justifications of French forces when they demanded the remittance of Đà Nẵng in 1847.