The roots of President Obama’s ambitious proposal for free community college can be found in a 2008 book by the economists Claudia Goldin and Lawrence Katz called “The Race Between Education and Technology.”

The book, a combination of economics and history, tells the story of how the United States built the world’s most successful economy by building its most successful education system. At the heart of that system was the universal high school movement of the early 20th century, which turned the United States into the world’s most educated country. These educated high school graduates — white-collar and blue-collar alike — powered the prosperity of the 20th century, Ms. Goldin and Mr. Katz demonstrated.

“The 20th century was the American century,” they wrote, “because it was the human-capital century.”