Fallout 76 is a prequel in the timeline of the Fallout franchise, which takes place in the region we call West Virginia.
Nuclear war has not been kind to anyone involved, and it will take more than just some great weapons and protective suits to survive. This combination of circumstances leads to a game environment where players can run into zombie-like human survivors, psychopathic robots, secret societies, and all manner of horrific monsters with mysterious origins. The technology that survived to assist players is a strange combination of 1950s optimism and alternative nuclear tech. In the franchise, some vaults were built for people to simply live and wait out the apocalypse, while others were constructed to experiment on the very people stuck within. In addition to the mutated people and animals caused by massive doses of radiation, there are hideout shelter 'vaults' that weren't always kind to the survivors.
As far as post-apocalyptic nuclear dystopian video games go, it's hard to get weirder than Fallout 76. Long-term fans of the Fallout franchise love the unpredictability that the post-nuclear war environment can bring.