Fallout is set in a timeline that deviated from between the end of World War II and the start of the Apollo program, where technology, politics, and culture followed a different course. While technology advanced, cultural and societal progress stagnated, giving the general world a Raygun Gothic appearance with advanced technology.
In the mid-21st century, a worldwide conflict is brought on by global petroleum shortage. Several nations enter Resource Wars over the last of non-renewable commodities, namely oil and uranium from 2052 to 2077. China invades Alaska in the winter of 2066, causing the United States to go to war with China and using Canadian resources to supply their war efforts, despite Canadian complaints. Eventually, the United States violently annexes Canada in February 2076 and reclaims Alaska nearly a year later. After years of conflict, on October 23, 2077, a global nuclear war occurs. It is not known who strikes first, but in less than two hours most major cities are destroyed. The effects of the war do not fade for the next hundred years, and as a consequence, human society has collapsed leaving only survivor settlements barely able to eke out a living in the barren wasteland, while a few live through the occurrence in underground fallout shelters known as Vaults. One of these, Vault 13, is the protagonist's home in Southern California, where the game begins in 2161, 84 years after the war.
Various tabletop implementations have been created to port the setting of Fallout to pen-and-paper roleplaying in a variety of systems.