Before the settlement of the Canadian West, which I date from 1896 to 1921, the Mounties established a series of forts. That’s where they exercised authority, enforced contracts and protected the property of settlers. Where Mounties were present, self-justice was rare. Canadians on the whole developed a less violent culture.

In recent research, I tested Mr. Pinker’s explanation by focusing on the settlement of the Canadian frontier — modern-day Alberta, Manitoba and Saskatchewan. Because it is Canada, I also looked at recent N.H.L. players from those areas to see if they carried a cultural baggage of violence to the rink.

To demonstrate the role of the Mounties, I compared settlements that in the late 1890s were near Mountie forts with those that were not. There are no homicide statistics for that period, but the 1911 census reveals male mortality patterns. Settlements far from the Mounties’ reach had more widows than widowers, suggesting unusually high adult male death rates. In fact, remote Canadian settlements during this period looked a lot like those of the Wild West. We do not know for certain why male death rates in these communities were high, but homicide is the prime suspect. After all, men kill other men more often than they kill women.

Even a century later, the violence in these areas continues. In 2014, communities at least 62 miles from former Mountie forts during their settlement had 45 percent more homicides and 55 percent more violent crimes per capita than communities closer to former forts. The distinction holds even when we take into account differences in population size and the level of urbanization. Given that the authority represented by the Mounties long ago expanded into every corner of the Canadian prairies, the persistence of this difference is surprising. Apparently in some remote and lawless areas, the Mounties arrived too late to prevent the development of a culture of violence.

In addition, those who live in areas that historically lay outside the reach of the Mounties are most likely to vote for members of the Conservative Party — the only party in Canada that opposes restricted gun ownership.