The Great War was the event that nearly destroyed the planet, and all of the people on it. The impact it had on the world was huge. Cities became piles of rubble, lakes became radioactive death pits, and some humans became little more than animals. There were many other side effects like; mutating animals and turning humans in to ghouls. Ghouls are humans that have been exposed to so much radiation that their body chemistry is changed so much that they are given mutations such as, being healed by radiation, making them live forever and being ugly as hell. Eventually, if they're exposed to radiation too long while 'ghoulified' they lose their ability to act like human beings and turn feral. But somehow, humanity survived it all. Most did so in great underground shelters known as Vaults.