This may seem like a dumb question, but why isn't there a standard currency throughout every country? Wouldn't that make everything easier?
I wander the same thing maybe It is just easier because some countries are poorer then others so money needs to be worth less.
For a currency, you need an issuing bank. Would you trust someone you cannot elect to issue your currency? The lack of people (politicians and citizens alike) saying yes leads to countries creating their own central bank. For most of history, the world did use one currency - gold. That said, because governments would often debase their currency, you would still have exchange rates I imagine.