What follows is a complete timeline of all-known canonical events in the Fallout universe. For clarity, sanity, and performance, some parts of the timeline were separated into other articles: Events unique to Fallout Tactics are found in Fallout Tactics timeline. Events unique to the canceled...
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Fallout's reality starts diverging from our own quite early (there's an alien spaceship in our orbit since the XVII century or something), but the biggest change is the USA splitting into a dozen "common whealths" in the 60s. Their first transistor only appears in 2023 (almost 80 years after us) but in 69 they had gone to the moon using only man-controlled actuators and instruments with mechanical computers. By ~2050 there's a massive energy crisis with oil reserves drying out all over the world, and that eventually leads to a war between the US common wealth and China which turns nuclear in 2077.
The first game takes place in 2161, 80-something years after the nuclear war destroys most of the planet's surface. In the games, the population is using left-over technology that had been developer until 2077.
That's why they're technologically so different from
us in the game.