Civil unrest consumed the nation from the 16th century onwards, and through it their independence gradually deteriorated. They had inherited the Mandarin feudal system from China, and went through the warlord & lawlessness earlier than China did.
By the 19th century, following a series of military conquests, Vietnam was integrated into French Indochina, and the French colonial period began.
This also brought the latin alphabet to Vietnam.
Previously, from about 200BC, Chinese pictographs had been used.