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.