As a vet who also suffers from PTSD, I find it fascinating to learn exactly how the mind works. The brain is a very complex, and remarkably flexible blob of nerve tissue. It's ability to improvise, adapt and overcome is second to none. I personally believe ones own experiences leading to the traumatic incident(s), will determine how we will deal with the trauma after. A comparison was made between wars prior to Korea, versus wars post Korea. Although there is no concrete evidence of this, I am of the opinion that part of the difference, is in the environment those people had been raised and the magnitude of the war. For example, WWII was fought by thousands of draftees that had survived the US depression. A certain "survival" mentality permeated throughout society. Couple that with the number who served, and you find a support network of people throughout society with similar experiences to yours. You went as a group. Came back as a group, hung out together, worked in the same factories, etc...
Starting with the US involvement in Korea, with few exceptions, small groups, or even individuals went for a specific period of time, and then left. No continuity of unit. no "misery loves company", if you will. Less of the population is affected, as these were the young teens during WWII. Jump another 10 years to Vietnam. Less units go as a group. More go as individuals, (as Facman stated), even less cohesiveness of unit. Add an element of tactical stupidity in the government, and a recipe for disaster is created. The average American is afraid of even acknowledging we're involved, for fear of verbal and sometimes physical assault by the war's opponents. Virtually no support network, vets won't even talk to each other.
Jump to my generation. All volunteer military, and by the time Operations Just Cause and Desert Shield/Storm come around, senior leaders and parents are mostly Vietnam vets. As such, there is a decided turn in support for our military. Units deploy as a whole, and stay until completion. Cohesiveness as a unit and esprit de corps is re-affirmed. However, we scatter piecemeal back into society. Little, to no, mental health support is available until the Vietnam vets start to demand it.
Since the start of the current conflict in 2003, the mental health care and recognition of PTSD has jumped by leaps and bounds. I know that the younger soldiers have become more open about the issues they face, and I offer myself as a therapist of sorts. If nothing else a friendly ear to bend. The health care providers have started to recognize more and more mental trauma and it's affect on society as a whole.
Mention was also made as to why there is no briefing prior to deployment or combat. I truly believe, if you tell people what they may suffer from, most will either desert or go AWOL to prevent it from happening. If you told someone that if they drove down a certain road, there was a 90% chance they'd wreck, they won't drive down it.