Roland August has officiated at thousands of weddings in Las Vegas, the self-proclaimed capital of “I do.”

But these days, August has a rare vantage point from which to observe the nation’s long shift toward “I don’t.”

Nevada’s marriage rate has plummeted in recent decades, an extreme version of a pullback happening across the U.S. The forces that have reshaped the nation’s economic life since the 1970s have helped make marriage an institution increasingly reserved for the well-educated and more affluent. Recent research suggests that the marriage gap is cementing disadvantage.

The wedding chapels where August works have seen business dwindle, he said, and Vegas is pushing to reverse the decline in an industry that generates as much as $3 billion in economic activity annually. In 2015 the surrounding county introduced a $14 surcharge on marriage licenses to pay for marketing. The effort is working against a broad national shift.

“Life has prioritized things differently,” August said.

Marriage has become a clear dividing line in a stratified country. Its decline is most pronounced among those who didn’t go beyond high school, as better-educated people tend to marry each other. America’s working and middle classes are faring badly, and the research points to unraveling families as one cause.

Half of Americans older than 18 were married in 2014, down from 72 percent in 1960, according to the Pew Research Center. The shift is more pronounced for the less educated, which is a loose proxy for income: As of 2014, almost 75 percent of women with bachelor’s degrees were married by their early 40s, while less than 60 percent of women with only a high-school diploma were.

Childbearing outside marriage also is affected by schooling. More than 70 percent of young mothers with only a high-school education had at least one child while single, according to Johns Hopkins University sociologist Andrew Cherlin. That was true for only about 30 percent of college-educated women.

Economic changes disrupted the traditional sequence of mating and marrying, helped by shifting mores. Women poured into the workforce in the late 1970s just as men grew increasingly unlikely to work. The Great Recession damaged prospects for the youngest lovebirds.

Men who marry drink less, work more and report greater happiness. Marriage allows couples to combine incomes, share costs and take advantage of tax breaks. Finally, children from stable, two-parent families do better in school and the job market, so today’s divide promises to entrench advantage or disadvantage.

Recent research showed that mortality is rising in middle age for less-educated white Americans, and authors Anne Case and Angus Deaton point to the move away from marriage as one possible factor.

“Both men and women lose the security of the stable marriages that were the standard among their parents,” they noted in a paper this year.

Still, not all the news is bad. Fewer marriages make for fewer divorces, for one thing. The U.S. marriage rate remains higher than that of many developed nations, including France, Spain and Italy.

Nevada hosts more weddings than any other state, and the number of licenses issued has stabilized, partly reflecting the rise of gay unions.

“People come here to have their wedding, and people come here to avoid a wedding,” said Oscar Goodman, Las Vegas’ former mayor. “Nobody should cry for Las Vegas.”