French colonization and occupation of the region was a consequence of missionary work of the 16th century, which had resulted in Catholics forming a converted minority. While Gia Long tolerated Catholicism, his successors Minh Mạng and Tự Đức were orthodox Confucians, admiring Chinese ancient culture. They forbid Catholic proselytism, as it was usually the religious arm of colonization[1] and they resisted European and American attempts to establish colonial trade posts, which France tried to impose against the laws of the country. This was seen by colonial powers as "provocative".
Confucian isolationist policy led the Vietnamese to refuse industrial modernization, so that they were not able to resist military power of a French invasion. In August 1858, Napoleon III ordered the landing of French forces at Tourane, (present-day Da Nang), beginning a colonial occupation that was to last almost a century. By 1884, the French had complete control over the country, which now formed the largest part of French Indochina. It took the Vietnamese people almost a century to expel the last colonial influence in their country.