Sven Böll, Christian Reiermann, Michael Sauga and Klaus Wiegrefe write for Der Spiegel.

It was shortly before his departure to Brussels when the chancellor was overpowered by the sheer magnitude of the moment. Helmut Kohl said that the "weight of history" would become palpable on that weekend; the resolution to establish the monetary union, he said, was a reason for "joyful celebration."

Soon afterwards, on May 2, 1998, Kohl and his counterparts reached a momentous decision. Eleven countries were to become part of the new European currency, including Germany, France, the Benelux countries -- and Italy.

Now, 14 years later, the weight of history has indeed become extraordinary. But no one is in the mood to celebrate anymore. In fact, the mood was downright somber when current Chancellor Angela Merkel met with her Italian counterpart Mario Monti in Rome six weeks ago.

Even as the markets were already prematurely celebrating the end of the euro crisis, the chancellor warned: "Europe hasn't turned the corner yet." She also noted that new challenges would constantly emerge in the coming years. Her host conceded that his country had not even overcome the most critical phase yet, and that the fight to save the currency remained an "ongoing challenge."

It didn't take long for the two leaders' concerns to prove justified. The Spanish economy has continued its decline, interest rates for southern European government bonds are rising once again, and election results in both Franceand Greecehave shown that citizens are tired of austerity programs. In short, no one can be certain that the monetary union will survive in the long term.

Many of the euro's problems can be traced to its birth defects. For political reasons, countries were included that weren't ready at the time. Furthermore, a common currency cannot survive on the long term if it is not backed by a political union. Even as the euro was being born, many experts warned that currency union members didn't belong together…