In the United States, a deep-seated sense of grievance about it has propelled Donald Trump all the way to the Republican presidential nomination. Not to be outdone, Hillary Clinton has placed tackling it at the centre of her own White House campaign. In Europe, it has been blamed for Britain’s Brexit vote, as well as for the rise of both far-right and far-left political parties around the continent.

There can be no doubt about it – in the West, rising economic inequality is the dominant political issue of today. Media pundits fulminate against its iniquities, Davos delegates debate its causes, would-be social justice warriors condemn its consequences, and academics who study it are accorded the unlikely status of “rock stars”. Where other political questions divide, inequality unites. The chattering classes are unanimous: rising inequality is a bad thing, and something must be done.

There is just one problem: inequality isn’t rising. Globally, income inequality has been falling for years, and by some key measures, the world has never been more equal. Viewed from Asia, this is no surprise. Since 1980, rapid economic growth in the developing world has allowed more than one billion people, mostly from Asia, to escape poverty and to join the rapidly swelling global middle class.

This transformation is most visible in China. Today, the fastest growing segment of China’s population is the class deemed “affluent” – with an annual household income of more than 140,000 yuan (HK$163,000). That might not sound much in developed economy terms, but goods and services are much cheaper in China than in the rich West.

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Apply the World Bank’s adjustment for this difference in purchasing power, and today some 200 million Chinese enjoy an annual household income of US$40,000 or more, not far behind the median US household income of US$54,000.

What’s more, the ranks of China’s affluent are expanding at a rate of some 25 million a year. With similar, albeit less prominent, trends visible in India, Indonesia, Vietnam and elsewhere, global income inequality is falling fast. Since 1980, the global Gini coefficient of income inequality between countries has fallen from more than 60 to less than 48 today. Other international measures of income inequality show similar, if less marked, declines over recent years. In short, the world is getting more, not less, equal.

So why are people in the West complaining so vociferously about rising inequality? The most commonly cited reason is the increasing disparity in Western countries between ordinary people and the tiny handful of the very wealthy, the infamous one per cent. It is true that the ultra-low, and even negative, interest rate policies pursued by central banks since the crisis have disproportionately benefited the asset-rich few. But this effect has been over-stated. Between 2010 and 2013, the richest one per cent of the US population saw their disposable incomes increase by 15 per cent in real terms. However, that increase only claws back earnings lost in the financial crisis, when their incomes fell 17 per cent.

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In any case, historically the politics of envy was never a major force in the US. Rather than condemning the rich, people generally aspired to emulate their success. This is the crux of the matter: no one resents wealth when incomes are rising for everyone. But in recent years, for the majority of people in the West incomes have stopped climbing. In fact they’ve gone into reverse. According to the Federal Reserve, in the last 15 years of the 20th century, the median US income rose 17 per cent in inflation-adjusted terms. In the first 15 years of the current century, it fell 7 per cent. Blue collar workers, and the majority of white collar workers, are no better off today than they were 20 years ago.

The reason incomes are stagnating for the working and middle classes in the rich world is simple enough. For most of the 20th century, incomes for the vast majority of people in the world were dictated by geography. If you were fortunate enough to be born in North America or western Europe, you automatically found yourself in the richest 20 per cent of the world’s population. That’s now changing. In the 21st century, incomes are being dictated less by accidents of birth, and more by skills.

Because of globalisation and technology, work that previously could be done only in the US or Europe can increasingly be done wherever it is most cost-effective. This shift first showed up in the outsourcing of relatively unskilled assembly line work to East Asia, but the trend is fast moving up the value curve. First it was factory jobs that moved to China. Then it was programming jobs that moved to India. Next – who knows? – maybe it will be surgeons in Africa operating on patients in Europe using remotely-controlled robotic scalpels.

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In a nutshell, the working and middle classes of the West now face competition, and they don’t like it. Competition holds down prices. The result is income stagnation in the West, and growth in much of the rest of the world as the citizens of developing countries approach rich country living standards. It should perhaps not be surprising that people in the developed world are aggrieved at this, and that they are increasingly turning to populist politicians who promise quick-fix solutions. But most Westerners are dishonest about the source of their grievance. It is not, as they claim, rising inequality. It is the exact opposite. It is actually increasing global equality that they dislike so much.