The United States is, by a long shot, the global leader in mass shootings, claiming just 5 per cent of the global population but an outsized share — 31 per cent — of the world's mass shooters since 1966, a new study finds.

The Philippines, Russia, Yemen and France—all countries that can claim a substantial share of the 291 documented mass shootings between 1966 and 2012 — collectively didn't even come close to the United States.

And what makes the United States such a fertile incubator for mass shooters? A comprehensive analysis of the perpetrators, their motives and the national contexts for their actions suggests that several factors have conspired to create in the United States a potent medium for fostering large-scale murder.

HARRISON MCCLARY A woman looks at a rifle in the trade booth showroom during the National Rifle Association's annual meeting in Nashville, Tennessee in April.

Those factors include a chronic and widespread gap between Americans' expectations for themselves and their actual achievement, Americans' adulation of fame, and the extent of gun ownership in the United States.

Set those features against a circumstance the United States shares with many other countries — a backdrop of poorly managed mental illness — and you have a uniquely volatile brew, the new study says.

With those conclusions, University of Alabama criminologist Adam Lankford set out to illuminate the darker side of American "exceptionalism" — the notion that the United States' size, diversity, political and economic institutions and traditions set us apart in the world. Lankford's paper is among those being presented this week at the American Sociological Association's annual meeting, in Chicago.

HARRISON MCCLARY / REUTERS Attendees visit the trade booths during the National Rifle Association's annual meeting in Nashville, Tennessee in April.

Perhaps no single factor sets the United States apart as sharply as does gun ownership, wrote Lankford. Of 178 countries included in Lankford's analysis, the United States ranked first in per-capita gun ownership. A 2007 survey found 270 million firearms in US civilian households — an ownership rate of 88.8 firearms per 100 people. Yemen followed, with 54.8 firearms per 100 people.

Across the world, countries' rates of homicides and suicides bore no clear relation to their likelihood of mass shootings in Lankford's analysis. In several countries with sky-high murder rates — Mexico, Venezuela and Nigeria for instance — mass shootings were extremely rare.

But the association between national firearm ownership rates and number of mass shooters per country showed clear statistical significance, he found. Behind the United States' top spot, Finland and Switzerland rank third and fourth, respectively, in per-capita gun ownership. While both countries enjoy vaunted reputations as safe places to live, both (along with No. 2 Yemen and No. 5 Serbia) ranked in the top 15 countries internationally for mass shooters per capita.

America's "gun culture," wrote Lankford, is deeply rooted in the idea that broad gun-ownership is a bulwark against the emergence of tyranny. And those roots continue to lie close to the surface, he wrote: A national survey conducted in 2013 found that 65 percent of Americans believe that the purpose of their right to bear arms remains "to make sure that people are able to protect themselves from tyranny."

But the American notion that individual rights must be protected against the state's powers comes at a cost. "Because of its world-leading firearm ownership rate, America does stand apart — and this appears connected to its high percentage of mass shootings," Lankford wrote.

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American mass shooters were also 3.6 times more likely to arm themselves with multiple weapons than were those who perpetrated similar crimes elsewhere, Lankford found. His analysis found that more weapons used in a mass shooting translated into more people killed. (Curiously, however, American mass shooters who carried out attacks using multiple weapons tended to claim fewer lives than did armed shooters elsewhere who did so.)

At the same time, mass shootings that took place in commercial spaces or schools were much more likely to have been carried out by American shooters than by those elsewhere, the new research found.

Multiple studies have explored the motives of mass shooters, and in these measures, too, Lankford suggests that uniquely American notions are powerfully at work.

He cites survey data showing that young Americans continue to embrace the "American dream" of soaring financial and educational achievement, of doing better than one's parents. When such dreams are frustrated, this bedrock belief in upward mobility predisposes some — especially those with a tenuous grasp on mental health — to psychological "strain". In rare instances, severe strain helps forge mass shooters, he wrote.

As powerful as the drive for material success is a newer American dream — a yearning for fame, wrote Lankford. By this American preoccupation, too, he suggests, frustrated strivers can be nudged toward mass violence.

"Increasingly in America — perhaps more than in any other country on the globe — fame is revered as an end unto itself," Lankford wrote. "Some mass shooters succumb to terrible delusions of grandeur and seek fame and glory through killing."

Eric Harris and Dylan Klebold, the perpetrators of the April 1999 shootings at Columbine High School in Colorado, both illustrate and feed such delusions, wrote Lankford: They both sought fame and gained infamy by their actions, and their example has been cited as inspiration by school shooters since, in Germany, Argentina, Finland and Canada.