Speculative musings, from an inadequate historical background.
We tend to take it for granted that the world looks like this, from a monetary perspective:
The world is divided into currency areas. Each currency area has one alpha bank (the king). All the other banks are beta banks (subjects, who follow the king). The beta banks promise to redeem their money for alpha bank money at a fixed exchange rate. The alpha bank makes no such promise the other way. Asymmetric redeemability. The alpha bank is the leader, who decides on monetary policy for the whole currency area. The beta banks just follow along, because they fix their exchange rates to the alpha bank. The world is divided into monetary monarchies.