How global currencies work past, present, and future by Eichengreen has a good history of currencies (from a European perspective). There were a few times when there were multiple currencies being used, and the ones used were the ones related to the countries who had the largest trade networks / 'colonies'. Of course credit was used a lot as well over long distances so folks didn't have to lug things around (Debt: the first 5,000 years by Graeber). Various cities vied between each other for the most transactions and business; Capitals of capital by Cassis has a modern era history.
Before that, gold and silver were often used as lowest common denominators internationally. See The power of gold: the history of an obsession by Bernstein for that. However metals weren't used everywhere: e.g., China used paper currencies for many years, and giant rocks where used in Micronesia:
Money: the true story of a made-up thing by Goldstein has a good pop-history overview.
Power often didn't come into play for currency choice, and neither did things "implode" as opposed to a gradual shifting in preference amongst currency users.
You start with an actual store of value that gets degraded over time through the people holding power over it (think mints). The coin starts with a high silver or gold content and with ever economic woe the ruler finds themselves in a new coin gets minted with some copper and tin added. Or just prints more.
Power comes into play as to dictating what currency people are forced to use. That the old coins had to be handed back in or dictating the adaptation. They implode when there is nothing backing it what so ever. At its core its Greshams law at work, with currencies or with other store of values.
If i am not mistaken Graeber has quite a few examples of this mechanism.
Before that, gold and silver were often used as lowest common denominators internationally. See The power of gold: the history of an obsession by Bernstein for that. However metals weren't used everywhere: e.g., China used paper currencies for many years, and giant rocks where used in Micronesia:
* https://en.wikipedia.org/wiki/Rai_stones
Money: the true story of a made-up thing by Goldstein has a good pop-history overview.
Power often didn't come into play for currency choice, and neither did things "implode" as opposed to a gradual shifting in preference amongst currency users.