US dollar is not just a currency, but also a weapon.
The greenback accounts for 63 percent of the world’s reserves. It is large and liquid; it has a reputation for safety and the rule of law, and its backers have the willingness to run account deficits. That is why most elected governments choose to hold the bulk of their reserves in USD. And that is how the US Federal Reserve becomes one of the leading world’s creditor, if not sole.