We HAVE destroyed ourselves before, and in fact science knows a fair bit about how it happened right in your neck of the woods. The Mayans overpopulated, exceeded the carrying capacity of the land, and then fought themselves into oblivion over the scraps that were left.
Turns out the same story has played out many times in the past, in many places around the world.
Read "Collapse", by Dr Jared Diamond, who also wrote "Guns, Germs & Steel".
I'm quite sure it will be the latter, which is why I'm spending my career developing a box that grows food efficiently enough to live on.
I believe that only by thinking inside this box will we have the freedom to leave oppressive or dangerous places and/or live in otherwise uninhabitable areas, underground, or even in space.
Otherwise, we end up like the Mayans, or the Easter Islanders- the biggest difference between us and them being that those civilizations and their contemporaries only had control over local or regional empires, while today's global technological reach will enable us to strip and ruin our entire planet, leaving no place and no one to start over.
The only way I can see the human race escaping this fate is through a box that grows everything from cannabis to cabbage, cheaply and most of all, reliably. And there isn't much time left.