America has been here before.

At the dawn of the 20th century, the economy was already well into a fundamental transformation of the labor force, as industry replaced farming and crafts as the primary source of new jobs. The shift was painful, spawning protest movements and political forces like progressivism. But the United States emerged from the turmoil far more prosperous and powerful.

Notably, the jobs of the new industrial economy were generally more productive and better paid than the jobs it left behind.

The nation is well on its way through a second transition, this time to a postindustrial economy with little factory work to be had. Even as industrial production has grown, the economy has shed seven million manufacturing jobs since 1980. Manufacturing’s share of employment has shrunk to 8.5 percent of nonfarm jobs from a peak of nearly 27 percent in 1920.

For politicians on the campaign trail and in Washington struggling to come up with a credible strategy to improve the fortunes of America’s understandably angry working class, that shift poses an unanswered question: Where will new, better jobs come from?