Europe, on the other hand — or more precisely the eurozone, the 18 countries sharing a common currency — did almost everything wrong. On the fiscal side, Europe never did much stimulus, and quickly turned to austerity — spending cuts and, to a lesser extent, tax increases — despite high unemployment. On the monetary side, officials fought the imaginary menace of inflation, and took years to acknowledge that the real threat is deflation.

Why did they get it so wrong?

To some extent, the turn toward austerity reflected institutional weakness: In the United States, federal programs like Social Security, Medicare and food stamps helped support states like Florida with especially severe housing busts, whereas European nations in similar straits, like Spain, were on their own. But European austerity also reflected willful misdiagnosis of the situation. In Europe as in America, the excesses that led to crisis overwhelmingly involved private rather than public debt, with Greece very much an outlier. But officials in Berlin and Brussels chose to ignore the evidence in favor of a narrative that placed all the blame on budget deficits, and simultaneously rejected the evidence suggesting — correctly — that trying to slash deficits in a depressed economy would deepen the depression.

Meanwhile, Europe’s central bankers decided to worry about inflation in 2011 and raise interest rates. Even at the time it was obvious that this was foolish — yes, there had been an uptick in headline inflation, but measures of underlying inflation were too low, not too high.

Monetary policy got much better after Mario Draghi became president of the European Central Bank in late 2011. Indeed, Mr. Draghi’s heroic efforts to provide liquidity to nations facing speculative attack almost surely saved the euro from collapse. But it’s not at all clear that he has the tools to fight off the broader deflationary forces set in motion by years of wrongheaded policy. Furthermore, he has to function with one hand tied behind his back, because Germany remains adamantly opposed to anything that might make life easier for debtor nations.

The terrible thing is that Europe’s economy was wrecked in the name of responsibility. True, there have been times when being tough meant reducing deficits and resisting the temptation to print money. In a depressed economy, however, a balanced-budget fetish and a hard-money obsession are deeply irresponsible. Not only do they hurt the economy in the short run, they can — and in Europe, have — inflict long-run harm, damaging the economy’s potential and driving it into a deflationary trap that’s very hard to escape.