Terrorists in Europe typically obtain their weapons illegally, and arms trafficking, a serious problem, is growing worse. In 2012, France increased fines and jail terms for possession and trafficking of illegal guns, but it’s unclear if that has had much effect. Recently, Interior Minister Bernard Cazeneuve vowed that he would present a new “aggressive” plan to fight illegal arms possession and trafficking. He said the authorities had seized nearly 6,000 weapons from criminal groups every year since 2013, of which 1,200 were military-grade weapons, numbers that pale in comparison to the number of similar weapons in circulation in the United States.

Limits on gun possession in France mean that people can go about their daily lives without fear of dying at the hands of shooters at school, stores or movie theaters. Data for 2012 compiled by GunPolicy.org found 140 gun homicides in France compared with 11,622 in the United States.

A few weeks ago, my mother attended a seminar on aging in Snyder Hall, the building where Mr. Harper-Mercer opened fire at Umpqua Community College, killing nine people and wounding nine more. Like everyone else in Roseburg, she’s still in shock, but she also told me that the community’s grief was unlikely to change people’s strong views on gun ownership. In the aftermath of the killings, she said, “There is a lot of talk around here that Obama is going to use this to take away our guns.”