The country is divided any which way you look at it. Some of it is generational, some of it is cultural, and some of it is geographic.

And some of it, it turns out, is what you might call educational. According to numbers cited by the New York Times earlier this month, young white American men without college degrees overwhelmingly support Donald Trump. Men and women without college degrees accounted for nearly half the electorate in 2012, or roughly 64 million people. According to the U.S. Census Bureau, nearly 97 million white people, 60 million men of a variety of races, and 23 million white men and women between the ages of 25 to 34 do not have an associates degree or higher. This gives some context for how many millions of young white men in the country have not gone beyond high school. Now this powerful demographic could determine the 2016 outcome. The Times‘s Nate Cohn doesn’t mince words: “It’s enough to keep the election close. It could even be enough for him to win.”

While we could ask why they support Trump, perhaps more telling is, why are there still so many of them?

Diagnosing why there are so many isn’t so simple. But a lot of it has to do with a series of economic and cultural issues from the last few decades.

Dewayne Matthews, the vice president of strategy at the Lumina Foundation, a private organization working to expand access to post-secondary education, offered several thoughts when I called him up. Since the 1980s, the number of young men who pursue higher education has increased only slightly; since 1991, women with college degrees outnumber men; in 2014, it was 34% to 26%.

And this situation is not unique to the U.S. The widening gap between young men and women with degrees is occurring in “all industrial and post-industrial countries,” Matthews said. “It’s spreading even into the developing world.”

“You’re talking about generations of families in communities that were build around a certain type of work.”

Why? “Structural shifts in the economy,” according to Matthews. In the early- to mid-20th century, the U.S. was an industrial nation where young men with a high school diploma could find jobs that earned them middle-class incomes. “You could get those jobs in a lot of sectors,” Matthews explained, citing manufacturing, natural resources, and forestry. “These were jobs that were held mostly by men—paid very good wages—and didn’t require post-secondary education.”