The Vietnam War was set in a very bad time for the United States. Its citizens were under the control of the Red Scare, a generalized fear of communism and possible communist spies. Combining this with the essential loss of the Vietnam proxy war with the Soviet Union, the United States came to a harsh realization that not all its battles would be victories. To be clear, the United States never actively engaged the USSR in Vietnam; it combated the communist ideals nurtured in Vietnam by the Soviets.
This would be "humanism". There were lots of enlightenment strains in the humanist movement, but overall the humanists championed the individual as a powerful entity.
