I think if everyone in the world uses a currency, the deal is easy. People are closer together. The gap between rich countries and poor countries will be reduced. Printing money machines is also easier. Facilitating many aspects: economy, life.
It would remove inefficiencies from the system, but the gap can't be shortened with just that. It could very well get larger.
Certain regions just have it much better in terms of natural resources, population size, and higher education standards, it all affects the population's productivity.
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One language. One purpose. One humankind.
Too many don't care for that. Something about us.