More than the Big Mac, Coca Cola, or Levi's 501 jeans, the dollar is surely the United States' signature export.

As for the single market, the E.U.'s landmark achievement, there is no question that a euro zone breakup would severely disrupt its operation in the short run.

Across the continent, political divisions are deepening. For all of these reasons, the specter of a euro zone collapse has not been dispatched.

Political union means transferring the prerogatives of national legislatures to the European parliament, which would then decide how to structure Europe's fiscal, banking, and monetary union.

The consequences of a collapse would not be pretty. Whichever country precipitated it - Germany by threatening to abandon the euro, or Greece or Spain by actually doing so - would trigger economic chaos and incur its neighbours' wrath.

While holding the eurozone together will be costly and difficult and painful for the politicians, breaking it up will be even more costly and more difficult.

The 24% unemployment reached at the depths of the Great Depression was no picnic.