[asfapifb]

This sounds like a good idea but it isn't (for now). Look up "Currency Areas". There are several economic factors that are essential to make a single currency successful. One of the downsides of a global currency is that if someone is indebted to someone else, they can't print money until the debt is paid. Not only that, but it creates issues when labor forces aren't liquid geographically and trade isn't free between places. The value of the currency will start to benefit some economies at the expense of others, leading to inescapable stagnation (this is one of Greece's problems).

FWIW many economists were skeptical of the Euro zone because it failed to satisfy some of the criteria of a currency area. This resulted in problems for some of its members following the 2008 crisis.