Why Do Historians Think That the Origins of the Vietnam

Why do historians think that the origins of the Vietnam War, in part, lie in the process of decolonization?

A) The division of Vietnam into antagonistic northern and southern states occurred after Vietnamese military forces had defeated the French, former governors of the region.
B) The North Vietnamese employed mercenary soldiers from various new postcolonial African states in a local war of liberation.
C) The United Nations, seeking to establish the postcolonial principle of national self-determination, encouraged North Vietnamese radicals to break with the West.