In addition, wars were once labor-intensive enterprises that absorbed the surplus temporarily, and sufficient numbers of those serving in the infantry and on warships were killed or seriously enough injured so that they could not add to the peacetime labor surplus.

The old ways of reducing surplus labor are, however, disappearing. Decades of medical and public health advances, as well as Medicare and Medicaid, have reduced the number of poverty-related deaths. The Iraq and Afghanistan wars have left many more service members injured than killed.

Over the past quarter-century, one very costly way of decreasing the surplus has been the imprisonment of people, mostly dark-skinned men, for actual and invented offenses. Felons are not often hired when they leave prison. Many, at least those who do not become recidivists, become surplus and then superfluous labor. As incarceration becomes less affordable for financially strapped states, inmates will reach surplus or superfluous status at a younger age.

Meanwhile, new ways of increasing surplus labor have appeared. One is the continued outsourcing of jobs to low-wage countries; the other is the continuing computerization and mechanization of manufacturing and of services not requiring hands-on human contact. Continuing increases in worker productivity add yet more to the surplus. So does the unwillingness of employers to even consider hiring people who have been unemployed for a long time.

When the jobless recovery ends and the economy is restored to good health, today’s surplus will be reduced. New technology and the products and services that accompany it will create new jobs. But unless the economy itself changes, eventually many of these innovations may be turned over to machines or the jobs may be sent to lower-wage economies.