I’ve been living in this country for most of the past 25 years, and I’ve been writing this column for the past 10 of them. Astonishing events have taken place in that quarter century: victory in the Cold War, the 9/11 attacks, two hot wars against Iraq, the most devastating economic and financial crisis since the Great Depression, and the election of the first black president.

But half obscured, something else has been going on. It’s insidious and so much part of the background music of daily life that, unless you’re directly affected, you barely notice it. But I would argue that it’s more important than any of the above for America’s sense of itself. I’m talking about the slow, seemingly unstoppable decline of America’s white working class.

Normally, such trends are the stuff of books, not of headlines. But last week came a headline that brought what’s been happening into appalling focus: it refers not to an individual tragedy but to an academic study, dry and scientific – yet also the distillation of tens of thousands of separate human tragedies. America’s white working class is dying. Literally.

The study was carried out by two Princeton professors, British-born Angus Deaton, the winner of this year’s Nobel Prize in economics for his work on poverty and consumption, and Anne Case (who is also his wife). It finds, quite astonishingly, that the mortality rate among white Americans, aged between 45 and 54 and without a university degree, has been rising, by 134 deaths per 100,000 in the space of the past 15 years alone.

British-born Nobel-Prize winner Angus Deaton was one of the authors of the study (Getty)

The figures alone are staggering. Deaton and Case calculate that if the death rate for that group had simply held at its 1998 level, almost 100,000 people would have survived. Had the rate continued to decline as it had over the previous two decades, some 500,000 more people would be alive today. The only recent peacetime equivalent is the number of lives lost to Aids – also around half a million.

No less remarkable, the trend is unique to America among the advanced economies. The most obvious explanation is economic hard times. But these were experienced everywhere; comparable death rates are still dropping in Britain and the EU, in Canada and Australia. And here it’s just the white working class. Death rates among US Hispanics and blacks in the same age and social class are continuing to fall.

Nor are the culprits the usual suspects, such as obesity, cancer or heart disease. The scourges of early 21st-century white working America tend to be self-inflicted: suicide, overuse of pain-killing opioid prescription drugs and excessive use of drugs and alcohol. The automatic assumption has always been that middle-aged blacks here were more likely to die from drug abuse than middle-aged whites. Not any more. And one last striking finding: whites with only a high-school education, among whom the death rate climbed by 22 per cent between 1999 and 2014, were overwhelmingly responsible for the increase. Among middle-aged white Americans with a university degree, the rate actually fell. So what is going on?

The answer, surely, lies in the slow decline of the US. The standard line has always been that that decline is relative – that while America is not as dominant as it once was, and rivals have been catching up, the country has been chugging along quite nicely. The work by Deaton and Case is further confirmation of what has long been evident. For some, the decline is absolute, among them working-class white Americans who are now worse off than they were in 1980.

There are far fewer decent jobs for less educated people, far fewer ways to claw oneself out of poverty. And, in this age of outsourcing, what decent jobs there are can vanish in a trice. Enfeebled trade unions are no longer able to resist the process. Nor do America’s healthcare and pensions systems, and a social safety net so much weaker than that of its foreign peers, offer much protection.

And then there’s the intangible aspect of decline. To a degree unmatched elsewhere, America’s white working class has been mythologised as the salt of the national earth, the human engine that turned the US into the greatest industrial power on the planet, that provided the home front that won two world wars.

Such is the myth. The contemporary reality is a country where badly paid service jobs are supplanting decent manufacturing ones, where the gulf between rich and poor is wider than at any point since the 1929 crash. For today’s white working class, it must often feel as if they’re the forgotten ones in a country obsessed with issues of race, gender and minority rights.

As jobs, pay and hope all dwindle, painkillers and alcohol – even suicide – make a terrible kind of sense <p> </p>

The politicians still prattle on about “helping hard-working Americans” and “restoring the American dream”. But even as instinctively optimistic a breed as the Americans now believe they are being sold a bill of goods. What dream? The reality is that no longer is it a hard-working blue-collar American’s birthright to live better than his parents. Most probably, he or she will be worse off.

Armchair psychology is a treacherous business, especially when countries are on the couch. But as jobs, pay and hope all dwindle, painkillers and alcohol – even suicide – make a terrible kind of sense. You think of the years around the demise of the Soviet Union, when so many Russians, deprived of both the old system’s vanished certainties and of hope for the future, drank themselves to death.

Of course, America 2015 isn’t the Russia of the 1980s and ’90s. But here, too, there’s a sense of betrayal, that the politicians have failed the white working Americans to whom they pay such lip service.