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

The work by Daron Acemoglu, Simon Johnson and James 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.”

The Turkish-born Acemoglu, 57, 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 call with the 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. “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. 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 U.S. and Europe are losing support from the public.

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

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

Johnson told the AP that economic pressures are 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,’’ he 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.”