Noah Smith, Columnist

Don't Forget What Causes a Recession

They have this nasty habit of showing up when least expected.

Just a matter of time.

Photographer: Mike Weaver/ABC/Getty Images

Remember recessions? Those times where the stock market goes down, unemployment goes up and businesses stop investing? There was a really big one about a decade ago, but that was a long time ago -- there are plenty of young workers now who were kids back when names like Lehman Brothers and Ben Bernanke were in the news. According to the indicators compiled by the National Bureau of Economic Research, the U.S. economy hasn’t been in recession since June 2009 -- almost nine years ago. If the economy sustains its expansion for just 14 more months, this will be the longest the country has gone without an economic downturn in recorded history, surpassing both the 1960s and 1990s booms in duration:

Why has the economy been growing uninterrupted for so long? Part of the reason is surely due to the severity of the Great Recession itself, coupled with the slowness of the subsequent recovery. The tremendous drought of business investment left the country with a backlog of office buildings and idle factories. And the deep dip in employment meant that it took a long time to put Americans back to work. The expansion that began in mid-2009 has really just been a long, plodding climb out of a very deep hole.