Europe is having a tough decade. It began with a still-unresolved sovereign debt crisis. Now terrorists have twice struck the Continent’s heart in Paris. What next?

The sequence isn’t yet clear, but I still think 2015 could be the year the euro dies. Last week’s Paris attacks further confirmed the European currency union is near its dénouement.

Back up a little. The euro currency zone is a subset of the larger European Union, whose founders envisioned it as an “ever-closer” free trade and immigration alliance. Is that what it is today?

No. United Europe is dis-integrating before our eyes.

Centuries-old cultural and linguistic differences are rising again. The nations that compose the European Union no longer trust each other. Without trust, there can be no permanent alliance.

Look what happened in Paris last Friday night. Within hours of the first gunshots, French President François Hollande closed his country’s borders. This was probably the right move under the circumstances. No one knew where else terrorists might strike that night.

Best to limit movement as much as possible.

Nevertheless, closing the borders would have been unnecessary had Hollande trusted his neighbors not to harbor additional attackers.

At the moment push came to shove, Hollande couldn’t trust his closest neighbors. He barred the doors and prepared to act alone.

If leaders like Hollande can’t trust each other to defend the union’s borders from outside attack, how can they possibly trust each other on relatively minor fiscal and monetary issues?

Answer: they can’t. That’s why their monetary union is doomed.

The best solution would be a planned, orderly return to national sovereignty and local currencies. A noble experiment didn’t work. No need to blame anyone; just admit it and move on.

That isn’t what will happen, of course. We will instead see an unplanned, disorderly breakup, quite possibly while the Continent is in the grip of internal violence and external war.

I thought the other Paris attack last January might lead that way (see "Charlie Hebdo May Have Changed Everything"). Hollande’s vows of reprisal suggests the process is under way.

This won’t end well for anyone, including the global economy. We have too many other question marks right now.

An imploding Europe is the last thing the financial markets need … but it may be what we get.

Patrick Watson is an Austin-based financial writer. Follow him on Twitter @PatrickW