Ryan_m_b said:
Nope, doesn't matter. I can think of plenty of books that never fully explain their past, often it feels a lot more real that way and adds a sense of mystery.
Well, let's be clear, it's up to you whether it matters to your story or not.
Some stories don't go into backstory, but it
can leave the story wanting of plausibility. You've got to decide if you want your story to have logical consistency. If the after effects of the downfall are significant to your story (and, by the sounds of what you're trying to set up with abandoned cities, they might be), you'll want to bring the reader up to speed on that. Otherwise, the story might be seen more as a kind of future fantasy rather than sci-fi.
It's a dreadful example, but I'll use it anyway:
The Hunger Games (books) were really interesting, but I would have enjoyed them more if they had done just a little backstory on the fall of 21st century civilization, and how we ended up with only 13 states, with most people in poverty and on the verge of starvation.
In this case, though, the milieu was the games themselves, which was more a microcosm, with its own internal logic and plot drivers. The landscape against which the Games themselves were set was secondary to the story.
On the other hand, an example of Ryan's "mysterious circumstances" is
Cloud Atlas, where they alluded to the downfall - without explaining it - for most of the book, and it was revealed in the course of the story. But is
was revealed.I put to you this litmus test:
Do you want your story to be about the aftermath of the downfall of civilization, and the characters' struggle against nature? Are the characters encountering historical evidence of the downfall?
Or do you want your story to be a microcosm in which they simply deal with the exigencies of day-to-day survival in a world they implicitly accept as their reality?
Perhaps more simply: do the
characters care about the history of their circumstances?