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

According to a study by Adam Lankford, a criminal justice professor at the University of Alabama, several factors have conspired to create in the United States a potent medium for fostering large-scale murder, including 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.

Lankford, whose paper is among those being presented this week at the American Sociological Assn.'s annual meeting, said that no single factor sets the United States apart as sharply as does gun ownership. 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 U.S. 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.

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.

Lankford 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."