PTSS almost seems like a culture-bound syndrome of the modern West.
There are significant confounders here, as modern science-based psychology got started around the same time - and WWI really was very different from earlier conflicts, not least in its sheer scale. But the idea is nonetheless intriguing; the West really is quite different from traditional societies, along lines that could plausibly make folks more vulnerable to traumatic shock.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.