Before? No, not so far (I'm probably 2/3 of the way in). It makes it sound like there was an explosion from a nuclear bomb or something, but it's vague. In the part where it happens, the father seems to know what's going on or is sort of prepared for it, so to me it implies that it was an ongoing war of some kind.
I haven't seen the movie - I had it from Netflix for like 3 weeks and was never in a mood to watch it.
edit: I'm going to take a break from the book for a little while since it's so depressing