Earth’s temperatures soared. Faced with the doomsday prospect of getting poached, charred and vaporised, governments agreed to joint pilot tests to move populations off surface. Companies raced to hollow out the mountains, constructing energy-sucking monoliths to sustain life underground.
Oceans started boiling over. Territorial disputes ensued and nations turned on each other. Finally, nukes flew. Survivors of the fallout fled to the mountains where the power struggle continues to this very day.