It seems to me that you have excluded some key factors by the way in which you have formulated the problem. I would suggest that you go back and think some about the boundary conditions you have given.

For instance, why does PTSD have to be related to industrialized warfare, or the West, or cultural constructs? Why can't it be related to the human psyche and the nature of extreme violence against others and what it does to the human spirit?

You're approaching the problem as a social scientist. Try to think outside your box and approach it as a theologian or psychologist. Think mind / heart / will / volition rather than moray / social framework / common deliverance of society / date and time.

Then, it might be that you are opposed to this given some set of pre-commitments you have, and I am not commenting on whether this is a good thing or not, just observing. The way you have formulated the problem is significant.

Another way of saying this might be as follows. You could take your thesis and conclude that since you have found evidence of ancient Japanese warriors who suffered from PTSD that it must therefore be related to warfare with a sword.

I'm not trying to be insulting, but rather just to challenge your basic set of presuppositions.