Fallout is a series of computer role-playing games originally produced and published by Interplay. Although set in and after the 22nd century, its story and artwork are heavily influenced by the post-World War II nuclear paranoia of the 1950s. The series is lightly based on the Mad Max film series. The series is sometimes considered to be an unofficial sequel to Wasteland, but it could not use that title as Electronic Arts held the rights to it. In particular, Brian Fargo, one of the original developers of Wasteland, is noted in the intros of Fallout, Fallout 2, and Fallout Tactics, with the caption "Brian Fargo presents", despite him not actually working on any of the games. Even though the Fallout series contains many references to items, persons, and scenarios found in Wasteland, the games are set in separate universes and are distinct from one another.
The background story of Fallout involves a "what-if" scenario in which the United States tries to devise fusion power resulting in the whole country becoming hegemonic and having less reliance on petroleum. However, this is not achieved until 2077, shortly after an oil drilling conflict off the Pacific Coast pits the United States against China. It ends with a nuclear exchange resulting in the post-apocalyptic world in which the game takes place.
Before the nuclear exchange took place, great underground Vaults were constructed across America, supposedly to protect the populace from the dangers of radiation. Although only 122 were constructed, over 400,000 would be needed to protect the entire nation. This is because the Vaults were not intended to save humanity; rather, they were social experiments being conducted by the United States government. Most vaults featured some variable to test how certain things influence people (and presumably the personal characteristics of the vault's occupants) such as Vault 69, which reportedly contained 999 women and one man.
Each installment of the series takes these facts as the context to the subsequent adventures: much of the landscape the player travels through is scarred with wreckage as well as radiation. These effects are not limited to the environment. Mutated survivors - those who lived through the attack outside a vault - are often physically unrecognizable as human. Even livestock - mostly represented by cows - are rarely if ever seen with fewer than two heads.