European financial markets were able to navigate problems of 9/11 and the Madrid and London bombings without too much instability, because they didn't have the extra layer of exchange-rate problems.

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.

For those unfortunate enough to experience it, long-term unemployment - now, as in the 1930s - is a tragedy. And, for society as a whole, there is the danger that the productive capacity of a significant portion of the labour force will be impaired.

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.

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.