My plot is basically centered around four people (Luci, Karynn, Kallie, and Jonathan) and their dog. They live in a very religious village set 100 years after something happened in America that mostly destroyed it. I wanted to see what y'all think about me not revealing what actually caused the catastrophe across America at any point in the book.
If you explained it in more depth then I could answer. I'll try anyway, you could treat it as one of those severe consquence secrets, some know, some speculate, and some simply chose to forget. Rather suffer in silence, then risk upsetting those around them. You could even drop subtle hints, an shifty group of people interested in the past, conflict with another community. I like the idea, theres a lot of potential.
Why would you not want to have what happened to destroy the USA (and presumably the world/civilization), even indirectly or in passing, revealed? There should be a pretty good reason for it. Also, if something happened in America, after 100 years, unless something happened elsewhere/everywhere, why wouldn't people from other nations move it--take over, revitalize the country--for it's space, resources, etc? There could be reasons--radiation, disease, chemical contamination, etc. But that would affect the current population--including the characters. Just a few random thoughts.