"In most modern factories it just takes a tiny fraction of the employees that were needed 40 or 50 years ago."

Even more importantly, the fewer employees in these factory jobs now require a much better education than the larger numbers of employees they replaced over the last few decades. The modern blue-collar employee is putting on more hats, working several sophisticated machines, and can cost the company tens of thousands or hundreds of thousands of dollars if they make a mistake programming or using those machines. Companies are not going to hire people off the street for those jobs even in periods of low unemployment.

This has all sorts of long-term side effects. Many people lament our 'service economy' and the marginalization of unions and blame our loss of industrial capacity for it, but the reality is that even a major resurgence of our industrial capacity is not going to bring back the unions or reduce the percentage of the work-force employed in our service economy, and not only because of the improvements in efficiency.

The reason is due to the shifting of blue-collar jobs into the higher ranks of the middle class. That is, modern blue-collar jobs needing significantly more education, for real. Unions don't appeal to more sophisticated workers (though there are exceptions such as the Pilot's union). Blue-collar jobs are filled more and more with people who would have been white-collar a few decades ago, but their requirements are very different. Hence the unions are dying away.

Similarly, the need for an educated workforce is creating a very wide gap between jobs on the low-end of the economic scale (e.g. window washer, restaurant worker) and what was formally a blue-collar job (assembly line worker) and is still called blue-collar today but wouldn't have been considered blue-collar a few decades ago (punching buttons on a computer, using hydraulically assisted tools, etc). The gap has become huge, one that requires a college education and cannot be overcome with only a year's worth of retraining to switch professions.

This, I think, is what is leaving a lot of Americans with nowhere to go even if they wanted to, and why job participation rates aren't likely to recover to prior levels even if the economy gets better. It will take another few generations for the work force to catch up with the work.

-Matt