This is an interesting idea - I do think that circumstances can enhance personality traits that are already there, or cause them to come out in a more negative way.
And I think my grandmother, who grew up poor in the Depression, had a touch of N-ism. But not so much as to be terribly destructive - she was definately a self-absorbed person, and nagged my poor Dad and Grandpa an awful lot, but neither of them seem to be ruined by it.
And my Dad is a Vietnam vet. I do think that after undergoing an intense negative experience, like being in a war, some people could react by temporarily becoming narcissistic. I was very young when he returned, and over the following years, he and my mother both showed some self-absorbed behavior. Not malignant or abusive - but when I think back it is clear that they just did not stop to consider the effects that their actions would have on their children. Mostly this took the form of some religious experimentation on their part, some of which was quite scary for a kid.
I used to be angry about this, but after I grew up a little and thought about the horrors my Dad must have seen at war, and the fear my mother must have felt, I realized that whatever they did was a way of coping with the aftermath of those experiences. But they got through whatever that was, settled down, and are now quite normal and loving.
Maybe this is another type of situational narcissism? I did read that after a traumatic experience, it is normal to be self-absorbed, as a person focuses on dealing with all their feelings and reactions. Anyway, great topic to explore.