A country could mine gold, pay with it for imports, and never have this gold brought back. Currently you can replace gold with oil: say, Saudi Arabia could lit

A country could mine gold, pay with it for imports, and never have this gold brought back. Currently you can replace gold with oil: say, Saudi Arabia could literally exchange many things it imports to oil, which can be nominated in USD to accommodate for the fluctuating monetary price of oil, but could be nominated in barrels directly, in a barter trade. They won't see this oil back, even e.g. as plastics made out of it, and they're fine with that. The US can (so far) replace the gold and oil with USD, in cash, investment, or even credit purchase form, because there's enough demand for US cash as a store of value and a currency to trade with non-US entities, and enough trust that the US is going to service its debt, so it's an investment. The US may (effectively) never receive much of these USDs it sends abroad back; they are still a good deal in an inflationary fiat-currency economy. This pump continues to work as long as things like Silicon Valley, Wall St, and the US military continue to be world-dominating in their respective areas. (And this is one reason why isolationism is a silly policy for the US, toxic for its economy.)