Europe's common currency, which was never a good idea, is nearing its expiration date. The coming year should seal the euro's doom — and the whole world will feel it.

The euro had a fatal flaw from the beginning. You cannot have monetary union without fiscal union. Otherwise, strong nations will take advantage of the weak ones and the weak take advantage of the strong.

The experiment "worked" for more than a decade only in the sense that it created export markets for Germany and France. Banks from those nations loaned euros to the so-called "PIIGS" (Portugal, Ireland, Italy, Greece and Spain), who then shipped the cash right back north by importing German and French goods.

This created an illusion of prosperity, not unlike the U.S. housing boom in which middle-class Americans bought unaffordable McMansions. In Europe's case, the common currency served to disguise the resulting imbalances. Now they must restore balance the hard way.

Greece and the other debtor nations have a stark choice: accept harsh austerity measures, or default and leave the eurozone. Growing populist movements are forcing political leaders to consider the inevitable. I think someone, probably Greece, will throw in the towel in 2015. Others will follow right behind. Then the whole alliance will collapse.

Something else will collapse, too: the German and French banks that will have to mark down the defaulted loans, sending the continent's economy deeper into deflation. Asian and U.S. banks will take hits, too, but they can probably survive. Some of Europe's best-known banks might not.

Just to make the year more interesting, economic sanctions on Russia are already backfiring on the West. Vladimir Putin's decision to cancel the South Stream gas pipeline killed what was supposed to be a major economic stimulus program in southeastern Europe. Look for more saber rattling from Moscow — and pressure from Washington for Europe to increase defense spending.

Not coincidentally, that same defense spending will boost revenue at U.S. aerospace firms. So will the coming Mideast war.

Another trend I expect in 2015 is frantic corporate efforts to fight off hacker attacks like the one rapidly reducing Sony (SNE) to a global joke. Top executives everywhere worry they will be next and there is very little they can do to stop it. Moreover, the potential damages are so huge and unpredictable that insurers won't cover them.

I said last week that 2014 was the hackers' breakout year. I think 2015 will be the year they break through — bringing down a major corporation.

Anything related to energy will have a rough year, too. I don't expect much recovery in crude oil prices, which means the fallout will keep growing. Local economies, companies and entire nations will see harsh adjustments.

If you thought 2014 was crazy, just hold on. 2015 will be even better.