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.

Why was there so much work-sharing in the 1930s? One reason is that government pushed for it. In his memoirs, President Herbert Hoover estimated that as many as two million workers avoided unemployment as a result of his efforts to promote work-sharing.

Southern Europe has not done enough to enhance its competitiveness, while northern Europe has not done enough to boost demand. Debt burdens remain crushing, and Europe's economy remains unable to grow.

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.

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.

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

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