One day things were normal. People were going about their business, everything seemed normal, and then everything seemed to go wrong. The Educating Very Illiterate Lemmings Corporation rolled out their crazy new discovery which intentionally created zombie like creatures... In retrospect maybe people should've been worried about EVIL Corp, but they didn't actually use their acronym... Also to be fair the lemmings did gain an increased grade point average. Then all the mega powers were infiltrated by the Illuminati who then nuked everyone. Some time around all this a vault company brought all their paranoid clientele... namely conspiracy theorists, mad scientists, and certain people who were alerted by the Illuminati and EVIL Corp.
So worldwide everyone was nuked with radiated zombies popping up everywhere, then the aliens came to Earth seeing everything undead and irradiated and decided to terraform the irradiated land and do some archaeology to figure out how the civilization failed. Then they missed a spot and got killed off by some irradiated zombies which created alien zombies. Thousands of years later certain structures made by humans that the aliens strengthened and maintained along with the alien structures were in ruins, but the radiation level was now low enough for human survival around the Earth. Thus the Vault Dwellers came out. A few Vaults being relatively normal. Others being a few mad scientists and mostly lab experiments, and others that were societies created to rule the world. Then again they hadn't expected that the zombies, irradiated zombies, and alien zombies had mutated into a weird community of sentient time immortal beings... Well at least some of them... others were just zombies that the sentient zombies didn't mind killing in self defense. In the end there were tons of little communities spread over the weird wasteland, and all sorts of crazy relics and technology from the previous civilizations... Along with the "experimental" tech developed by some of the Vault Dwellers.
Most communities were of a single type of Wastelander although there were a few communities with mixed types. The normal human zombies called themselves vampires. They didn't seem to age, they didn't like sunlight on their rotted beings, and they thought it made themselves seem more interesting. The irradiated zombies called themselves the Stars and most of the other groups tried to distance themselves from them. Then the Alien zombies just called themselves the collective as there were so many different alien species. The illuminati and EVIL Corp picked survivors ended up creating a kinda facist power hungry world dominating civilization that called themselves Great Order Overseeing Dudes or GOOD. Although with the state of the world they weren't getting anywhere fast soon. Most of the mad scientists ended up hooking up together and creating what was more or less their version of the internet... and it was usually used to share knowledge and information that could lead to new inventions or good ways to get experimental subjects. Plus with no laws other than "Don't test on other scientists" they didn't have to pay mind to anything like "Ethics". Then finally there were the general joe schmoes who were in the vaults that tried to settle and recreate a somewhat normal looking society. They just called themselves Humans as that's what they were.
Finally there was the group that wasn't really a group but everyone called the Fetuses. Young pure groups that were still underground and just waiting to be brought up into the world. Vaults that had yet to open for whatever reason, undead that had survived the alien terraforming but were buried underground (both sentient and not sentient), and Aliens that had created Vault like things of their own.
The stage has been set now we take a look at the life of...