In Last of the Annamese, South Vietnamese Marine Colonel Pham Ngoc Thanh explains to the protagonist, Chuck Griffin, that he has no money to buy tickets for his wife and son to escape from Saigon before the communists take the city. Eventually, he tasks Chuck with evacuating them when he stays behind to face the North Vietnamese.
Thanh is incorruptible in a society riven by corruption. The habit of private citizens giving money to public servants for their carrying out their obligations went back centuries. The accepted way of doing business was that the government paid functionaries so little that, to survive, they were forced to sell their services. It was so commonplace as to be unremarkable.
Thanh’s pay as a colonel is paltry. He is expected to siphon off the salaries of his subordinates, exact taxes from the civilian population, and accept payment for protection. But Thanh, a monk turned warrior, refuses to participate in such practices. As a consequence, he is dirt poor. He’s used to poverty. His family, before the communists murdered them, were poor dirt farmers.
One of the causes of the fall of South Vietnam was poverty driven by corruption. The Viet Cong (really the North Vietnamese) exploited the situation with great success. Some U.S. personnel in-country, as early as the beginning of the 1960s, saw what was happening. They were at a loss to ameliorate the situation. The collapse of South Vietnam, under the pressure of the communists, was inevitable.