MONEY IS AN INSTRUMENT OF GOVERNANCE as well as commerce. It enables citizens to participate in the economic life of their societies while reminding them where political authority resides and where their loyalties belong. So it has been since ancient times, when visages of Nebuchadnezzar and Caesar were stamped on the coins of their realms, and so it is today. In almost all 195 countries on Earth, the change in people’s pockets and the banknotes in their wallets are an assertion of national sovereignty.
But today there is an exception to that general principle: the euro, which is the common currency of 18 of the member states of the European Union. The eurozone puts them in the vanguard of the greatest experiment in regional cooperation the world has ever known.