system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 what would happen if there only existed one currency in the world.
gpt
It most likely will never happen.  Look to the Euro-zone to see what happens on a smaller scale.  By having the Euro, individual countries lose control of their money.  Spain can't print Euros because everyone else will get angry at them.  Countries that are run poorly (such as Greece) drag down the countries that do well (such as Germany).  There's so many problems with a shared currency, countries are prideful and diverse, and giving up control of your money is a very hard thing to convince countries.