Marty Feldstein nailed it spot on in this piece:

That was the purpose of the 1992 Maastricht Treaty, which established the European Union. The influential report “One market, one money,” issued in 1990 under the leadership of the former French Finance Minister Jacques Delors, called for the creation of a single currency, relying on the specious argument that the single market could not function well otherwise. More realistically, advocates of a single currency reasoned that it would cause people to identify as Europeans, and that the shift to a single European Central Bank would herald a shift of power away from national governments.

The problem with the Euro is that it is an attempt to impose political unity, conformity and identity through economic pressure, not merely a currency.  As such, it was born with inherent defects that have now emerged and will remain.