Just as some of us live longer than others, countries have different average life expectancies. At the bottom of the scale is Swaziland, the only country in the world where a newborn still cannot expect to reach age 50. And at the top is Hong Kong, where a newborn can expect to live to age 84.

In 1960, the world’s countries could be divided into two groups, based on mortality. Countries in one group had low average life expectancy, from 28 years in Mali to just under 50 years in El Salvador. And countries in the second, much less populous group enjoyed higher average life expectancy — up to 73 years in Norway, Iceland, the Netherlands and Sweden.

Since then, Hong Kong has surpassed this North European group, as have Japan (84 years), Italy (83), Spain (83) and Switzerland (83). Today, the people of Hong Kong can expect their children to live 17 years longer than in 1960. Japanese newborns can expect to live 16 years longer; and newborn Icelanders can expect to live 10 years longer.

Much of this increase in life expectancy around the world is a result of declining child mortality. And the increase has been more marked for women, who tend to live an average of three years longer than men. In Iceland, for example, the average life expectancy for men and women is 81 and 84, respectively.

But life expectancy can also vary significantly within countries, between rich and poor. According to a recent study by two MIT researchers, the wealthiest 1 percent of American men tend to live almost 15 years longer than the poorest 1 percent; and the wealthiest 1 percent of American women can expect to live 10 years longer than their poorer counterparts.

Moreover, this gap widened over time. In just the last 15 years, the average life expectancy of the wealthiest 5 percent of Americans has increased by two years for men, and three years for women. Over the same period, the average life expectancy of the poorest 5 percent Americans has increased by just three months for men, and hardly at all for women.

Like recent reports about many Americans’ deteriorating health, this difference in life expectancy seems to reflect not just income and wealth inequality but also unequal access to health care. And yet U.S. President Donald Trump and congressional Republicans seem intent on depriving 23 million more Americans of health insurance by repealing and replacing the 2010 Affordable Care Act (“Obamacare”).

If they succeed, life expectancy in the United States would most likely continue to decline, relative to other developed countries. Between 1960 and today, for example, average life expectancy in the U.S. increased from 70 to 79 years, whereas in Italy it increased from 69 to 83 years. While the average American lived one year longer than the average Italian in 1960, the average Italian now lives four years longer than the average American.

Average U.S. life expectancy has increased more slowly than in Europe partly because many white middle-aged Americans have, since 1999, been living shorter lives, owing to lifestyle-related diseases, opioid overdoses and suicides. In fact, since 1981, opioid overdoses alone have taken almost as many lives in America as the HIV/AIDS epidemic.

It is extremely rare for any large cohort in a modern society to suffer such a decline in life expectancy. The only other time it has happened in recent decades was in Russia after the collapse of communism, and in Africa after the outbreak of the HIV/AIDS epidemic.

Rising inequality, then, is not just a question of income, wealth and power; it is, literally, a matter of life and death. This may explain why inequality has shot to the top of the political agenda in the U.S. and Europe in recent years. In his 2016 Democratic primary campaign, Vermont Sen. Bernie Sanders, a self-proclaimed socialist, condemned America’s rising inequality and came closer to being elected president than many had expected. And Trump — like the “leave” campaign in Britain — was embraced by many voters who feel left behind.

Despite being founded in 1945, the International Monetary Fund only recently began to pay ample attention to the distribution of income and wealth in its member countries. Having now realized that inequality can hinder economic growth, the IMF has begun to discuss the inequality-growth relationship with several of its members.

Some observers have disparaged the IMF for this new approach, and argue that increased inequality simply reflects what people have voted for. But those who claim that inequality is something to be desired are akin to those who argue that unemployment is always voluntary, as some economists still insist.

In fact, when inequality rises, democracy suffers, which is why the demotion of the U.S. in one prominent ranking of the world’s democracies is not particularly surprising. Most people do not want to be unemployed, or be left behind, or have his or her life cut short. It only looks that way to those who frame the choices voters make.

Thorvaldur Gylfason is a professor of economics at the University of Iceland. © Project Syndicate, 2017