Mayans

It wasn't so long ago that they were the most powerful and technologically advanced civilization in the Americas. But gradually over time, the combination of incessant wars, prolonged droughts, unsustainable resource extraction, and lack of a reliable water source caused their society to utterly collapse. You can read a good account of it here. I only mention this because, you know, our shit stinks just as bad as the Mayans'---only our collapse will be much, much harder. There's probably still enough time to turn the ship around, but we'd better think about doing it soon!

---Baron V