...AND RICHER...:

[A]fter thousands of years of most people on the planet living as serfs, as slaves or in other destitute scenarios, half the population now has the financial means to be able to do more than just try to survive.

"There was almost no middle class before the Industrial Revolution began in the 1830s," [Brookings Institution scholar Homi Kharas] said. "It was just royalty and peasants. Now we are about to have a majority middle-class world."

Today, the middle class totals about 3.7 billion people, Kharas says, or 48 percent of the world's population. An additional 190 million (2.5 percent) comprise the mega-rich. Together, the two groups make up a majority of humanity in 2018, a shift with wide-reaching consequences for the global economy -- and potential implications for the happiness of millions of people.

So how much money does it take to meet Kharas's definition of middle-class? It depends on where you live and, more precisely, on how expensive things are where you live. Kharas's definition takes into account the higher cost of meeting basic needs in places such as the United States, Western Europe and Japan than in much of the developing world.

In dollar terms, Kharas defines the global middle class as those who make $11 to $110 a day, or about $4,000 to $40,000 a year. Those are per-person numbers, so families with two parents and multiple children would need a lot more. It's a wide range, but remember that he adjusts the amounts by country to take into account how much people can buy with the money they earn. For example, earning $12,000 for a family of four in Indonesia would qualify for the global middle class, but it would not in the United States.

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