For the development team, some things were obvious.
Fallout creator Tim Cain recently decided to discuss the game's lore again. He explained that the developers didn't write some things down in the design document and simply assumed that "X is true."
They weren't talked about directly, there's no special cutscene, record, or NPC that would say "Look, event X happened here." The developers' vision was supported through narrative and level design, as well as NPC behavior.
Tim clarified that his reasoning is technically not canon — now Bethesda decides what is.
The creator recalled how a few years ago in an interview he stated that the Great War was started by China dropping the first nuclear bomb.
Then the interviewer was surprised by this statement, and Tim was surprised by his reaction. The developer himself considered it "obvious" and it was a revelation to him that there had been disputes about the first strike for many years.
Tim Cain explained why the developers then assumed that China launched the first nuclear strike::
"In the original game, the US created the FEV virus [Forced Evolutionary Virus], conducted biological weapons research. They weren't supposed to do that. Moreover, the US signed a UN treaty that it wouldn't do that. And I think you can find that in the game. "
China discovered that the US was doing this. How? Espionage. They learned that the US was continuing the research, and the US said: \"Oops, we're guilty. We won't do that anymore.\" However, in reality, they continued, simply moving the research to another base, and that was the hidden base where you discover the ZAX supercomputer.
So he knows some of this, and there are logs that explain it [...] when China learned that the US was still [working on the virus], they tried to use diplomacy and espionage, but none of it worked. So they just launched a nuclear strike. The US retaliated. Other countries launched nuclear strikes because all they saw were missiles flying.
Technically, China started [the Great War] by launching the first nuclear bomb. But you could argue that technically the US started it by conducting illegal biological weapons research and then repeatedly lying about stopping it."
