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 1992 crisis proved that the existing system was unstable. Not moving forward to the euro would have set up Europe for even more disruptive crises.

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

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.

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.