Valéry Giscard d’Estaing, the former French president, called it America’s “exorbitant privilege”. Others use a rather blunter term – the “tyranny of the dollar”.

Whatever the description, the upshot is not in doubt; ownership of the world’s dominant reserve currency has conferred enormous economic and geopolitical power on the US, reinforcing its command over world affairs.

All great empires have at their heart an imposing means of exchange; an internationally pre-eminent currency is very much part of their social and political hegemony. An effective coinage was central to Rome’s military power, helping to keep far flung lands subservient. In more recent times, it was the British pound, but...