This is a great commentary about recent Greece struggle with European Union, by comparing the EU to the US.
… For a currency union to handle widely divergent economies, they must be deeply integrated across multiple dimensions.
… The mechanisms include large fiscal transfers– by necessity currency unions are transfer unions.
… Another reason U.S. states don’t pop out of the dollar area is that they (with the exception of Vermont) have to balance their operating budgets.
… The euro was never conceived as an end in itself. It was created as a means toward greater growth and unity. It has failed badly on both counts. If U.S.-style integration is politically unrealistic, then the only hope for long-term stability is a slimmed-down euro area of more homogeneous countries.
… eventually they must choose: Either integrate far more deeply, or help the euro area’s most troubled members escape.
Reference: Europe’s Insane Deal With Greece