The recession lies at the heart of this. In research drawing on millions of anonymized tax returns, the Berkeley economist Danny Yagan has found that for every percentage point a local unemployment rate increased during the downturn, individuals were 0.4 percentage points less likely to be working in 2015. The intensity of the recession, in other words, squeezed workers out of the labor market. Moreover, as the Great Recession dampened employment, it also dampened earnings, with higher increases in a given area’s jobless rate leading to lower earnings there nearly a decade down the road.

More broadly, the downturn seems to have wiped away demand for certain types of work, skewing the jobs market in a way that has hurt the middle class—a middle class for whom wages only recently started increasing again, and a middle class that has been shrinking since before the Great Recession hit. Job losses from the downturn were concentrated in so-called “middle skill” jobs—ones that require more education than a high-school diploma, but less than a college degree, things like parts manufacturing, assembly, telemarketing, mail delivery, cooking, and administrative-support work. “Unemployed middle-skill workers … appear to have few attractive or feasible employment alternatives outside of their skill class, and the drop in male participation rates during the past several decades can be explained in part by an erosion of middle-skill job opportunities,” one study found—arguing, in effect, that middle-class jobs were washed away and workers decided to give up rather than taking a fast-food or big-box retail gig.

Those jobs were washed away, economists have found, by employers using the recession as an opportunity to fire workers and invest in labor-saving machines. One look at recession-era data found that employers were much more likely to add skill requirements to their job-vacancy postings in areas with big unemployment spikes: Instead of asking potential workers to have an associate’s degree and three years of experience, say, they would ask applicants to have a bachelor’s degree and five years of experience. At the same time, those businesses in hard-hit areas would invest in machines that would reduce the need for human workers at all. All together, the effect was that the Great Recession hastened the economy toward rewarding better-educated workers and robots, to the detriment of people without an advanced degree.

These changes in the demand for work and the jobs available have caused income inequality to be worse now than it would have been otherwise. Indeed, the rich have rebounded completely from the recession in terms of unemployment, earnings, and total job count—they did so quickly, in fact, and have flourished through much of the recovery. It is the middle class and lower-income workers who have not. “The employment and earnings impacts were most negative for those with low 2006 earnings, indicating that the Great Recession caused a long-term increase in employment and earnings inequality not only within but also across skill levels,” Yagan has found.