Are you saying that you don't believe that depression is unheard of in community/extended family-based cultures (there's probably some official term but I don't know what it is) not because depression doesn't exist there, but because its underreported? That could certainly be true. In America, its become acceptable and even in some cases fashionable to acknowledge depression, while in other cultures it might be very stigmatizing.
Anyway, depression is different from legitimate grief. In your example, the grief would be profound, it would be shared, it would be a very traumatic experience for the entire community, especially the parents of children who died, but that is not depression.
Well, no, I didn't think of it all as underreported. As a person who has had depression a good deal of my life, I can tell with certainty that it wasn't based on whether or not I had family around to mitigate it. I believe that a lot of depression is chemically/biologically based. And yes, there is a difference between grief and depression, but grief can trigger depression. Even if there are others there to share said grief.
I'm not saying everyone who experiences trauma would end up depressed. If that was true, gosh, the human race would have suicided itself off a long time ago. But some might be more prone to depression than others. *I* would become depressed in the children-being-killed-off scenario, most likely. I don't think of it as a fashionable, in-vogue diagnosis (although many do... it can be trendy to be depressed, heh) and I certainly don't think it's anything to be PROUD of. I think it's something to fight and something to move past - as any other illness.
And you're right - it CAN be culturally based - someone who is lonely or even bored might equate that to depression in our culture, whereas in other cultures, they wouldn't. They might use completely different terminology, or might not even acknowledge it at all. But from my experience with it (both on a personal level, seeing it in my loved ones, and from studying it from an academic point of view for quite a few graduate courses... it's not always simple to dismiss as "this person needs more community". That CAN be a part of the cure, and it's often helpful to turn outside oneself instead of doing a bunch of navel-gazing... but it's not always that simple. And again I'll say that I believe that depression has biological roots (and/or components). If your brain chemistry is off for some reason, all the extended-family togetherness in the world isn't going to be enough to mitigate that.