Fallout 1 and 2 were actually about preservation of status quo. It didn't change the Wasteland, it prevented it from changing. Change happened off-screen, gradually. Fallout 3 was actually about changing status quo with all this purity stuff, but I didn't play into epilogue yet to see implications if any are present.
I'll put it this way. Fallout 1 and 2 changed things, mostly because the events in the game were so large that they couldn't be stopped simply be defeating the bad guy... Fallout 3 SHOULD have but they wimped out (Seriously the closest to a confirmation is a RUMOR...)
Fallout NV is about the fate of a single town.
And Fallout 4 completely unalters things because it wipes the slate clean AND gives an excuse why it can never affect anything outside the game it exists in.
The CLOSEST to Fallout 4 possibly having an outside effect is Fallout 3's reference to a Canadian Institute.
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Basically imagine if in Fallout 1 they revealed that Super Mutants all had a bomb in their chests that would blow up in a year AND that they found a cure for virus that creates them and immunized the world.
That is... basically Fallout 4. You can actually just completely skip it.
Which isn't a bad thing, it really comes down to taste... but it feels like such a waste to not add on some lore... and to instead just try as hard as they can to be as self-contained as possible. It is like they absolutely refuse to let the setting change.