This point brings us to the question: How does a currency become an international currency? The question is particularly intriguing because, in the reign of fiat currencies, its answer is unlike the explanation of how a currency becomes dominant within a country.
When gold, silver, or other commodities were the normal means of exchange, units of currency were defined by commonly understood weights of the commodities that circulated. Soon the equivalent of warehouse receipts for precious metals circulated as currency. Under a commodity standard more generally the value of paper currency or any other financial claim is derived from the value of the standard.