>>713080923
>just look at the bottlecap trade
The bottlecaps as a currency were explained in 1 and new vegas as being a water-backed currency used by Hub merchants, which worked because of the cap's ability to store value; being a pre-war artifact that's common enough to be liquid, but not so common as to be worthless, and the lack of infrastructure to make new bottlecaps keeps inflation manageable and prevents counterfeiting.
As the world of fallout progressed from 1 to 2, society had developed enough to the point where gold coinage, the traditional store of value for basically all of human history, were able to supersede the bottlecap as a currency, and the NCR would later switch to paper banknotes, backed up by the NCR's gold reserves.
The reason, covered in New Vegas, as to why the bottlecap returned to being the primary medium of account and unit of exchange for the wasteland is because, during the NCR-Brotherhood war, the Brotherhood destroyed the NCR's gold reserves, thus forcing them to issue fiat currency that suffered rapid inflation, and thus, especially in frontier areas where the NCR can exercise less control, the NCR dollar fell out of favour as traders were less convinced of its worth as a store of value, thus switching back to the water-backed bottlecap. Caesar's Legion, not having these hangups, continues to mint and issue commodity money, which, that and a few other articles, like the bill of sale in Jeannie May's safe, imply a degree of technological and societal sophistication we don't really see in the actual game. Time cuts, unfortunately, strike again.
In Fallout 3 and 4 there is no actual explanation or justification for the bottlecap as a currency other than "Because fallout 1 did it."
