Have always wonder which currency would the world accept if only one currency was to be used. Maybe the dollar?, don't think so, The British won't tolerate that.
Cryptocurrency?. Maybe. Until the advent of cryptocurrency, I never thought that would be possible but it seems possible.
The world is not too far from a unified currency.
States have their own currencies because it is tied to their economies. As a general rule, states issue currencies for the amount of material assets in circulation on the territory of this state. The currency of another state cannot replace the state's own currency. In international relations, you can use a single currency by agreement of several states, however, only their own currency can circulate within the state.
Therefore, the idea of a single currency for all states cannot be implemented in practice.
Well explained, generally speaking all states have their own currency it's symbolizing the capabilities of such place.
Whatever currency the government established around its jurisdictions needs being supported and followed by the citizens residing
around the place, The idea of single currency may happened digitally but with traditional fiat it's still far to reality.
Government wants to control the jurisdicted vicinities.