even though it came out in the mid 80s, mccarthy began writing the book in the mid 70s, when the war was still fresh in everyone's memory. one character has a necklace with an ear on it, and that was a major scandal during the war, that american GIs were making necklaces out of the ears of vietnamese people. if i recall correctly american military brass had an obsession with kill counts and confirmed kills, so GIs just began doing My Lai shit because once someone is dead it is very easy to say they were a combatant; similarly, the glanton gang soon realize that mexican scalps are indistinguishable from Apache ones so they begin indiscriminately killing mexicans too. the filibustering gang that the kid joins at the beginning, to cross the border and continue the war illegally, is kind of similar to the US actions in Cambodia and Laos.

like i said, i need to reread the book, and mccarthy surely intended it to be more than just a vietnam allegory, but i think there is enough there for somebody to make a masters' thesis or something out of it.