Fallout 3 is a science fiction set in post apocalyptic world caused by an extension of the cold war during the 1950s. The player experiences the future wasteland, centuries after 1950s nuclear war, filled with early Cold War iconography, including songs by bands like The Ink Spots and propaganda posters in the style of post-WWII government messages. Much of the game's visual design is referencing 1950s and 1960s sci-fi novels and early sci-fi films.
The game doesn't just visually represent the period through it's design, "Fallout 3 is also trying to subvert any kind of nostalgia of the 50s by presenting a landscape that existed in the minds of all those who could do no more than sincerely get under their school desks during bombing drills." - fjohnrickert