When I worked for the VA I saw the records of quite a few soldiers who didn’t see combat but who had PTSD. Many were in medical services far from the front. A couple were WWII veterans who worked at the Bikini Atoll site. Lots worked with explosives and weaponry, tanks, etc. A few were soldiers attacked in some manner by other soldiers on their base. In all the time I worked with the VA I never once came across someone who was simply a stateside clerk (or similar) who had PTSD. I very much doubt, after filing and compiling several hundred Compensation and Pension Examinations, that someone who didn’t have PTSD would be given a diagnosis of PTSD simply on their say-so.
PTSD was indeed prevalent after WWII. Heck, the villains in every Hollywood movie in the late 40s and 1950s were guys screwed up by the war. Perhaps you’ve heard of John Huston’s Let There Be Light documentary, or the Oscar-winning Best Years of Our Lives. After WWI, shell shock (one of the old names for PTSD) was a huge issue, so much so it’s cliche—the UK alone treated 80,000 cases of shell shock. Wynn already mentioned earlier examples. And diarist Samuel Pepys wrote about PTSD-type issues back in the 1600s, when soldiers coming back from war were often considered too messed up to function properly in society. Plato has a famous reference to “only the dead have seen the end of war,” in a screed written about how veterans behave after war, and Socrates wrote plays about what we now call PTSD.
If anything is invented here, it’s not PTSD, it’s your very convenient groups of friends who always manage to prove whatever resentful, petty little point you’re trying to make. You resent everyone all the time, 24 hours a day, 7 days a week, including (or especially) on holidays.