All manner of experiences can cause PTSD–rape,murder, disasters like Katrina, but exposure to combat is overwhelmingly the primary cause of this acute and often untreatable disorder.
Notwithstanding the bogus precision of the DSM and its list of PTSD symptoms, I would argue that combat-induced PTSD remains both poorly understood and under-diagnosed. No one has a clue about the actual incidence of PTSD in either of the two world wars, partly because it was not yet a bonafide psychiatric diagnosis, and partly for the same reason it remains woefully under-diagnosed to this day: that is, if the scrofulous old men who cause wars and declare wars allowed the citizenry to fully comprehend what actually happens–psychologically, emotionally, and spiritually–to the legions of young men they send off to fight their unjust wars, there might be a true anti-war movement, based not on politics but on horror and revulsion against war.
From Turgenev’s 1861 novel, Father’s and Sons, a line which is lamentably appropriate to the whole PTSD tragedy:
“The true horror, gentleman, is that there is no horror.”