30% of the world's mined gold exists underground Manhattan, and you can take tours!
"You can tour the trading rooms, the museum and the Fed's vault, which holds 900 tons of gold."
In many ways, war gave rise to capitalism and not vice versa.
Modern coinage and money arose largely out of the enormous challenge of feeding and paying a medieval army.
Kings would print money and distribute it to their populace, then ask for some of it back. Markets arose out of the need to pay this tax, and it benefitted soldiers who had lots of spending power. So it was governments creating the markets, not regulating them once they'd come to fruition.
Additionally, it was unwise to do business with armed passerbys with IOUs, so cash was the logical material of exchange, especially since the soldiers had most likely recently looted some gold/silver/whatever on their way to visit your humble market.
Precise exchange rates were born of violence, for instance to stem a blood feud, exact legal damages were conferred, and substitutions were made when necessary. Otherwise, most trades were conducted with rough equivalency, with shame or death as a possible punishment for underhanded-ness.
Also the anarchism of Barcelona
also the war debt that is circulating from the king of england and the british bank notes that act as IOUs