Donald Trump won the presidential election for many reasons: He came across as a strong leader and resonated with people who wanted change; Hillary Clinton was a deeply flawed status quo candidate who created her own email troubles and then couldn’t get past them; she took her Upper Midwest “blue wall” for granted while he campaigned aggressively there; and his white rural voters turned out in droves while her urban, suburban and minority supporters didn’t.

But the single biggest reason Trump won the Electoral College by about 100,000 votes in previously blue Michigan, Pennsylvania and Wisconsin (as well as in swing states like Ohio and North Carolina) was the overwhelming support of white, working-class voters who don’t have college degrees.

Exit polls conducted by the Pew Research Group showed that “Trump’s margin among whites without a college degree [was] the largest among any candidate in exit polls since 1980. Two-thirds (67%) of non-college whites backed Trump, compared with just 28% who supported Clinton, resulting in a 39-point advantage for Trump among this group. … The gap between college and non-college whites is wider in 2016 than in any past election dating to 1980.”

And the more education people had, the more likely they were to vote for Clinton: Clinton won all college graduates by 49%-45% and those with postgraduate education by 58%-37%. She improved a lot on President Obama’s 2012 performance in 48 of the country’s 50 most well-educated counties, Nate Silver noted, but did much worse in 47 of the 50 counties that had the lowest percentage of college grads. And since only a third of Americans over 25 have college degrees, the math was against her.

I write this not to cast judgment (I come from a blue-collar background and neither of my parents went to college), but simply to point out how stark the fault lines are in American society. “Social class, defined today by one’s level of education, appears to have become the single most important social fracture in countless industrialized and emerging-market countries,” wrote historian Francis Fukuyama in The Financial Times.

In the 21st century, education determines people’s economic status and shapes their worldviews. There are plenty of exceptions to these “rules,” but in general the more education you have, the more opportunities you get, and the more income you make, the more likely you are to live in cities and have more liberal, cosmopolitan views.

Let’s look at economic opportunities first:

• In November’s jobs report, released last Friday, Americans over 25 years old who had at least a bachelor’s degree had an unemployment rate of only 2.3% — half the overall percentage — and 73.7% were in the workforce. Among those with high school diplomas, 4.9% were unemployed, and their labor force participation rate was only 57.8%, below the average of 62.7%.

• According to the Bureau of Labor Statistics, median annual earnings for full-time workers who held bachelor’s degrees or higher was $65,832 in the third quarter, 80% more than the median annual earnings of $36,400 for full-time workers who had high school diplomas.

• Earlier this year, the Center on Education and the Workforce at Georgetown University found that 8.4 million (more than 70%) of the 11.6 million jobs that had been created at that point in the U.S. since the Great Recession went to people who had earned at least a bachelor’s degree. High school graduates got only 80,000 of those jobs, a mere 0.7%. “The recovery has been virtually nonexistent for less-educated workers,” the authors wrote.

Is it any wonder these people feel left behind by the economy? They have been, and their worldview reflects it.

Thomas Byrne Edsall, one of the sharpest analysts of class in America, wrote in The New York Times about research done by the Institute for Advanced Studies in Culture at the University of Virginia, which studied whites who had college degrees (whom the researchers called the “Social Elite”) and those who didn’t and also were religious conservatives (the “Disinherited”).

Among the “Social Elite,” 73% described their financial situation as “good” or “excellent,” while eight in 10 expected their future to be at least as good. Three out of four thought the economy was getting better and almost the same number said you can still get ahead by working hard. They also mostly trust the government and said they’d vote for Clinton by 74%-14%

Nearly three-quarters of the “Disinherited” believed they could no longer get ahead by hard work and that the federal government threatened their freedom. More than half saw their economic condition as “poor” and likely to get worse. They said they’d vote for Trump by — wait for it — 74%-14%.

You rarely get divisions this stark. What you see depends on where you stand, and in a 21st-century information-based economy, skills and education increasingly separate the haves from the have-nots. Trump and Brexit were only the beginning.