I will give you a little unwritten history of Viet Nam. I was assistant ncoic of security at Tan My LORAN station near the village ofTan My. Our planes and ships used it for radar navigation. When the top man was gone, I was in charge. We had some locals doing menial work on base. Encluded was a sweet teenage girl named Bien who I spoke to every day. My job was to protect people and equipment. I was concerned about non military working on base, but it was set up before I got there by people above my pay grade, so I kept quiet. One night the Viet Cong raided the village and killed all those who worked for us to set an example, encluding a sweet innocent teen age girl. This has haunted me every day of my life for the last 50 years.
This was Colonel Kurtz's point In Apocalypse Now. You could not defeat an enemy who had the will to do horrible things like that but you're not willing to do those horrible things as well. We did horrible things like that during WW2 (indiscriminate bombings of civilians, etc). We have not been willing to do that since then without punishing those who have done so. Obama, for instance, would not allow bombing ISIS oil storage tanks because of the pollution it would cause. Perhaps that is the reason we haven't conclusively won a war since WW2?