STOCKHOLM (AP) — The Nobel memorial prize in economics was awarded Monday to three economists who have studied why some countries are rich and others poor and have documented that freer, open societies are more likely to prosper.

The work by Daron Acemoglu, Simon Johnson and James A. Robinson “demonstrated the importance of societal institutions for a country’s prosperity,” the Nobel committee of the Royal Swedish Academy of Sciences said at the announcement in Stockholm.

Acemoglu and Johnson work at the Massachusetts Institute of Technology, while Robinson does his research at the University of Chicago.

Jakob Svensson, chair of the Committee for the Prize in Economic Sciences, said their analysis has provided "a much deeper understanding of the root causes of why countries fail or succeed.”

Reached by the academy in Athens, Greece, where he was to speak at a conference, the Turkish-born Acemoglu, 57, said he was astonished by the award.

“You never expect something like this," he said.

Acemoglu said the research honored by the prize underscores the value of democratic institutions.

“I think broadly speaking the work that we have done favors democracy,” he said in a telephone call with the Nobel committee and reporters in Stockholm.

But, he added: “Democracy is not a panacea. Introducing democracy is very hard. When you introduce elections, that sometimes creates conflict.”

In an interview with The Associated Press, Robinson, 64, said he doubts that China can sustain its economic prosperity as long as it keeps a repressive political system.

“There’s many examples in world history of societies like that that do well for 40, 50 years," Robinson said by phone. “What you see is that’s never sustainable. ... The Soviet Union did well for 50 or 60 years.''

Robinson said many societies have successfully made the transition to what he, Acemoglu and Johnson call an “inclusive society.’’

“Look at the United States," Robinson said. “This was a country of slavery, of privilege, where women were not allowed to take part in the economy or vote.”

“Every country that is currently relatively inclusive and open made that transition," he added. "In the modern world, you’ve seen that in South Korea, in Taiwan, in Mauritius.’’

Acemoglu and Robinson wrote the 2012 bestseller, “Why Nations Fail: The Origins of Power, Prosperity, and Poverty," which argued that manmade problems were responsible for keeping countries poor.

In their work, the winners looked, for instance, at the city of Nogales, which straddles the U.S.-Mexico border.

Despite sharing the same geography, climate and a common culture, life is very different on either side of the border. In Nogales, Arizona, to the north, residents are relatively well-off and live long lives; most children graduate from high school. To the south, in Mexico’s Nogales, Sonora, residents are much poorer, and organized crime and corruption abound.

The difference, the economists found, is a U.S. system that protects property rights and gives citizens a say in their government.

Acemoglu expressed worry Monday that democratic institutions in the United States and Europe were losing support from the population.

“Support for democracy is at an all-time low, especially in the U.S., but also in Greece and in the UK and France,“ Acemoglu said on the sidelines of the conference in an Athens suburb.

“And I think that is a symbol of how people are disappointed with democracy,” he said. “They think democracy hasn’t delivered what it promised.''

Robinson agreed. "Clearly, you had an attack on inclusive institutions in this country," he said. “You had a presidential candidate who denied that he lost the last election. So President (Donald) Trump rejected the democratic rule of the citizens. ... Of course, I’m worried. I’m a concerned citizen.”

Johnson told the AP that economic pressures were alienating many Americans.

“A lot of people who were previously in the middle class were hit very hard by the combination of globalization, automation, the decline of trade unions, and a sort of shift more broadly in corporate philosophy,'' Johnson said. "So instead of workers being a resource to be developed, which they were in the 19th and early 20th century, they became a cost to be minimized ... Now, that squeezed the middle class.’’

"We have, as a country, failed to deliver in recent decades on what we were previously very good at, which was sharing prosperity,'' Johnson said.

One key for the future, Johnson said, is how societies manage new technologies such as artificial intelligence.

“AI could go either way," he said. "AI could either empower people with a lot of education, make them more highly skilled, enable them to do more tasks and get more pay. Or it could be another massive wave of automation that pushes the remnants of the middle down to the bottom. And then, yes, you’re not going to like the political outcomes.’’

In their work, the economists studied institutions that European powers such as Britain and Spain put in place when they colonized much of the world starting in the 1600s. They brought different policies to different places, giving later researchers a “natural experiment" to analyze.

Colonies that were sparsely populated offered less resistance to foreign rule and therefore attracted more settlers. In those places, colonial governments tended to establish more inclusive economic institutions that “incentivized settlers to work hard and invest in their new homeland. In turn, this led to demands for political rights that gave them a share of profits,” the Nobel committee said.

In more densely populated places that attracted fewer settlers, the colonial regimes limited political rights and set up institutions that focused on “benefiting a local elite at the expense of the wider population," it said.

“Paradoxically, this means that the parts of the colonized world that were relatively the most prosperous around 500 years ago are now those that are relatively poor,” it added, noting that India’s industrial production exceeded the American colonies’ in the 18th century.

The economics prize is formally known as the Bank of Sweden Prize in Economic Sciences in Memory of Alfred Nobel. The central bank established it in 1968 as a memorial to Nobel, the 19th-century Swedish businessman and chemist who invented dynamite and established the five Nobel Prizes.

Though Nobel purists stress that the economics prize is technically not a Nobel Prize, it is always presented together with the others on Dec. 10, the anniversary of Nobel's death in 1896.

Nobel honors were announced last week in medicine, physics, chemistry, literature and peace.

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Corder reported from The Hague, Netherlands, and Wiseman from Washington. AP reporters David Keyton in Berlin and Elena Becatoros in Athens contributed to this report.