Comment by kortilla

That’s not how that works. If Japan needs USD it goes to the forex market. That market represents a massive trade flow.

It doesn’t matter which currency you pick in that world apart from capital control. As long as it’s reasonably stable you flow through it with many billions of dollars a day with ease. The conversions are effectively free because the spreads are tiny.

Using the US dollar to trade between two countries that are not to US does nothing to the the currency. It just shifts a deficit.