The end of the world occurred pretty much as we had predicted. Too many humans, not enough space or resources to go around. The details are trivial and pointless, the reasons, as always, purely human ones.
The earth was nearly wiped clean of life. A great cleansing, an atomic spark struck by human hands, quickly raged out of control. Spears of nuclear fire rained from the skies. Continents were swallowed in flames and fell beneath the boiling oceans. Humanity was almost extinguished, their spirits becoming part of the background radiation that blanketed the earth.
A quiet darkness fell across the planet, lasting many years. Few survived the devastation. Some had been fortunate enough to reach safety, taking shelter in great underground vaults. When the great darkness passed, these vaults opened, and their inhabitants emerged to begin their lives again.
One of the northern tribes claims they are descended from one such Vault. They hold that their founder and ancestor, one known as the "Vault Dweller," once saved the world from a great evil. According to their legend, this evil arose in the far south. It corrupted all it touched, twisting men inside, turning them into beasts. Only through the bravery of this Vault Dweller was the evil destroyed. But in so doing, he lost many of his friends and suffered greatly, sacrificing much of himself to save the world.
When at last he returned to the home he had fought so hard to protect, he was cast out. Exiled. In confronting that which they feared, he had become something else in their eyes...and no longer their champion.
Forsaken by his people, he strode into the wasteland. He traveled far to the north, until he came to the great canyons. There, he founded a small village, Arroyo, where he lived out the rest of his years. And so, for a generation since its founding, Arroyo has lived in peace, its canyons sheltering it from the outside world. It is home. Your home.
But the scars left by the war have not yet healed. And the Earth has not forgotten.