It's often a hopeless cause, but I like to try to reconcile Bethesda's choices with older points of lore that they may have disregarded or behaved strangely toward.
Caps being the universal currency is one. I doubt there's a good explanation for why they're used all over the country, when they are backed by water Merchants in California.
Pure coincidence, then, is the only reason that everyone, everywhere, just happened by luck to choose caps as currency.
Sigh, oh well.

So, in comes my head-canon, unofficial lore I "assume" in my own games.
How long had the Brotherhood been in DC when the Lone Wanderer came onto the scene? Could they have brought a water merchant representative and technician with them, to secure a water source for themselves, and thereby ended up starting the caps economy? It would seem like a smart thing to do when going so far from home.

I'd mod F4 myself, but there are so many times that "caps" are spoken out loud that it could never be done perfectly.

But that being said -- imagine an alternate reality, where the brotherhood and caps never did come to the East coast.

What kind of money might have been used between Rivet City and and Megaton? I'm not sure they had any gold mines or printing presses.
In the older Fallout, the Brotherhood actually had their own currency.
What about the Commonwealth? Would Diamond city, the Institute, Good Neighbor, etc, be using the same currencies? Couldn't the Institute just mass produce whatever currency the surface is using, and utterly obliterate the economy faster than a synth armada? So they would have to switch to something that couldn't be easily duplicated, and that's a short list.

Or just use barter.

Well, it is hard to think of any viable currency in a world without governments and (most importantly) central banks. As with everything, I assume bottlecaps just caught on with post war society and obviously proved to be simpler than hauling tons of goods around.

Of course it is rather strange that it spread across the whole continent, I assume it was mostly just laziness on Bethesda's part to stick with the old money from F1 and F2. They also did away with the barter system from the old games, which made a more sense in that kind of society imo.

In FNV we see NCR and Legion introducing their own money, with regulations and guarantees to control the value of their currency (NCR makes their own paper money and the Legion mints them from gold and silver). I was pretty happy about that, because it was the first time the problem was adressed in a Fallout game, though it sadly didn't have any gameplay importance at all.

To answer the hypothetical question: If they never introduced bottle caps as a currency in the east, I guess they would have continued to use pre war money or something similar to bottlecaps like ammunition, which also has real value next to the accreted one.

Caps were really only a thing in fallout 1. In 2, NCR currency was making its appearance. Caps were only a thing because it was the choice of the hub water merchants.
Caps in the east can only be one of three things: Bethesda just said so, or total and pure luck that everyone, everywhere randomly chose the same junk item, or that the water merchants of the hub have somehow influenced the east coast.
Admittedly, if the water merchants did have access to DC, they'd very quickly become insanely rich if they weren't wiped out, and would easily control the new currency. But that access seems unlikely. But then all the same factions and monsters being in the east coast happened anyway.
It's odd that we found all the same creatures and groups on the east coast in DC, except for the one faction that actually would have made the setting make sense, caps-wise.

It would have been interesting if they approached currency like that one town in Wasteland and Metro where ammo is your money.

We know that people do travel the continent in the fallout universe from characters such as Kellogg and Harold. With bottle caps being readily available to everyone post war, hard to replicate and with people travelling from settlement to settlement I don't find it too unbelievable that they have been adopted by everyone in the wasteland as currency. Look at the real world, many cultures have historically used precious metals such as gold and silver as their currencies. I simply see bottle caps as the post war equivalent.

The exact same piece of junk, everywhere? That's an incredible,astounding coincidence. The odds of it happening in every corner of the country, independently... that's incredible and strange.
If I starting picking up bottlecaps, how would I convince anyone to give me food for those caps, even post-war? That kind of scenario had to happen, everywhere, almost at random, somehow. All across the country, everyone just said, "Yeah, I'll give you food for that garbage you just picked up." Nah, I don't buy it, it's Bethesda's laziness.

I agree that it is a bit of a stretch, I'm just saying it wouldn't be entirely impossible for the wasteland to adopt the bottle cap as a standard currency.

What I think happened:

Caps were established as currency by the Hub many, many years ago, before Fallout 1 even began. The first caravans were operating out of the Hub back before either Harold or Grey had been exposed to FEV, so pre 2100's. The Hub was at least established by then, so I'd say caps have been about since then. The Hub had enough influence that Richard Grey, an exile from Vault City, found out about the place and wound up there all the way from Nevada. In fallout 1, despite many people having little clue of settlements a few miles up the road from them, everyone knows about the Hub. It was probably one of the first human settlements established post war.

Hub caravans have been operating across the wastes for 200 years, mainly on the west coast, but their influence could likely be felt across the wasteland. As more caravans began operating it's likely they adopted the Hubs operating system. Places like New Canaan prospered as trade towns, so it's likely they adopted the Hubs systems. Their caravans would carry them further east as well.

It's also worth noting, caps a merely a place holder, as a readily available marker of value. Most wasteland trading is barter. The NCR and Legion are the only nations that try to implement a true monetary system that transcends the Barter system, but most trade still operates that way. Caps are valued as a currency, yes, but they are readily available. You could trade purely in cigarettes, or pre-war money if you really wanted and wouldn't be much worse off for it, outside of credit checks which require caps, but once again, caps are plentiful, difficult to replicate due to lack of manufacturing tech and skill, and as such represent a very sustainable currency. Trading in bullets wouldn't work because bullets are readily manufactured an used, cigarettes can be produced post war and smoked. Caps on the other hand serve no other purpose. Making them perfect currency.

I also liked shoddycasts' idea, that a straggle of caravans from the west followed the Brotherhood east, which brought goods like Jet to the West. That of course is kind of hard to imagine, considering they would likely have passed many other trading locations on the way, and travelling that far is difficult even for the Brotherhood. Not to mention this would have likely occurred mid-Brotherhood War, so why would they even tolerate traders following them? But still, Jet on the west coast is far more of an issue than bottle caps.

I personally doubt the BoS started the economy. There's no point for them to do that. The Brotherhood remain very aloof from most wasteland affairs and the only thing they really seem to be concerned with is fighting super mutants, a far bigger issue than starting a currency.

Personally, it's never bothered me. I can head canon explain that it's merely the influence of a very dominant culture spread east. It's been 200 years near enough since the Hub has been operational, and many thing on the East coast, from caps to Jet, or even tales of a junktown jerky vendor, suggest that the influence of the West Coast can be felt even here, after all, there are many thing we have here in the UK that come from nations on the other side of the world, that we don't even realise are foreign import, or aspects of a foreign culture, we just accept them as part of our lives. At least 180-170 years at least have passed since the Hub began operation. It took the Brotherhood roughly a year to get from the west coast to the east. I can believe that the influence of the Hubs economic system could spread across the wastes via caravans. Caravans are after all the lifeline of the wastes. Every games has them, every major civilisation or settlement is reliant on them, and they've been operating since well before Fallout 1 began. So yeah, I can believe that caravan traders could spread that economic system across the wasteland in nearly two centuries.

Yeah I favor the idea that the Brotherhood would have brought hub water merchants with them to the east, and that Hub through the BOS or their own efforts over time, are actually a very far reaching group.

I imagine, like a couple of others have said, that caps simply spread across the continent. When they started being used in the West, I suppose people realised that they were an effective currency. The backing of the Water Merchants got weaker as the practice spread East, but they simply became the status quo.

The world of Fallout is a water-based economy, isn't it?

Bottlecaps in fallout 1, backed by water. If they hadn't been backed by water they would have just been garbage. In Fallout 2, it was ncr dollars, backed by gold.

Sirdanest wrote:

Bottlecaps in fallout 1, backed by water.  If they hadn't been backed by water they would have just been garbage.  In Fallout 2, it was ncr dollars, backed by gold.  

Funny how they advanced enough to go from basic necessity-based economy to a gold-based economy. It really tells you how far they came along from Fallout 1 to Fallout 2.

Yeah, they went a VERY long way in 80 years. From a little village to a town with forcefields and modern-looking police and tree-lined roads.
But they were vault dwellers with a geck. It seems all they needed was real security and then could use their expertise and technology to take off.