The war, known now to the survivors as The Fury, was devastating. As many as could be saved were moved into underground habitations built for this very eventuality. Not everyone was lucky enough to have a place in the shelters, and when the leaded doors were closed and sealed, many people were left to fight for survival in the gloom, as the radioactive and mutagenic haze played strange tricks with the light of the sun and moon, and death burrowed into their bones.
The species survived, though, and in those underground redoubts, so did civilization. The old nations were forgotten with time and new ones formed, as fresh tunnels linked farflung bunkers. They only need to wait and endure. Eventually, the scientists said things might be safe, and so scouts were sent outside.
They were not prepared for what they found. The natural world, as they had hoped, had healed itself. There was no trace of the world that had been or the war that destroyed it. Things were lush and green--though that didn't mean all the horror or strangeness it was gone.
There were people on this new Earth, apparently the deformed descendants of those who had been left outside. Dwarfish ones one had perhaps come from makeshift bunkers not sufficiently sealed as they too spent much time underground. People of the forest, grotesquely thin and large eared, and then the most numerous people who lived in primitive cities. All of them were hideous. There was sometime neotenic about them in a way that made the skin crawl: their teeth were so small, their foreheads flat, their jaws receding.
Councils were convened to consider this information. The technological know-how of the people was superior to their mutated cousins, but they were limited in their access to resources and many of their machines had broken down. They were, ironically, fewer in number than those who had survived the terrors of fallout.
The decision was made not to wage an all out war for the surface, but instead to look for out of the way places to recover resources. They would approach the mutants, when necessary using similar technology--they could not afford to have any more advanced devices fall into the primitives' hands. They could perhaps surreptitiously influence them, maybe create allies to prepare for their return. Some might have to die, of course, but perhaps the more could be shepherded toward civilization.
It would be a long project, but humanity was up to it. For now, they would have to embrace the name "orc" given to them by the mutants and play the expected role.
