TORONTO — Last summer I taught a course at the University of Toronto called “American Tragedy: Guns and Mass Shootings in U.S. History.” One memorable day, my 20 mostly Canadian students reflected on the frequency of mass shootings in America and how these calamities don’t receive much public interest unless the gunman claims several lives. One student remarked: “Reading about this stuff makes me so sad. It also makes me happy to live in Canada, where we don’t have to worry about this kind of thing.”

As an expatriate from California, I have felt this same sense of gratitude many times. Watching news reels and Twitter feeds about the next mass shooting back home, I would reflect that Toronto seemed immune to the kind of gun violence that I had witnessed and written about in Los Angeles and Philadelphia.

However, several gun attacks here this summer have made me, and many Torontonians, question that sense of exceptionalism. Mass shootings are no longer a uniquely American problem.

The latest occurred last week when, the police say, Faisal Hussain, 29, fired on diners sitting at outdoor tables along the Danforth, a bustling neighborhood near downtown. Reese Fallon, an 18-year-old woman set to study nursing this fall, was killed, as was Julianna Kozis, a 10-year-old synchronized swimmer. Thirteen more people were hurt. The city has also been gripped this month by allegations that a Toronto man killed at least eight people and buried them on property where he worked as a landscaper.