The world has one global currency, I think it's impossible. To make everyone have the same thought is impossible, and surely there will always be those who oppose or support, and it will be difficult to make one global currency.
I think you're not aware but there's already a currency which is rule the world. Its "Dollars". If you're thinking that bitcoin can become global then i should advice your to stop watching dreams because it will never happen.
"Rule"? How can you say that dollars are ruling the world? Do you know that US has a lot of debts? It may be a good country but it has a lot of debts. The reason US dollars are always involved in trading or investing, it is because US dollars is the most used or traded fiat currency. It is not ruling the world, peoplr are just used on trading this fiat so they just this currenc y as the basis or the value of crypto currencies. Also, if that is the ruling fiat, that shpuld have the most expensive val of all fiat, but it is not..