What we should be trying to understand is not one single event but why we have so many of them. The number of deaths by firearms in the United States was 32,000 last year. Around 11,000 were gun homicides. …

The data in social science are rarely this clear. They strongly suggest that we have so much more gun violence than other countries because we have far more permissive laws than others regarding the sale and possession of guns. With 5 percent of the world’s population, the United States has 50 percent of the guns.

There is clear evidence that tightening laws — even in highly individualistic countries with long traditions of gun ownership — can reduce gun violence. In Australia, after a 1996 ban on all automatic and semiautomatic weapons — a real ban, not like the one we enacted in 1994 with 600-plus exceptions — gun-related homicides dropped 59 percent over the next decade. The rate of suicide by firearm plummeted 65 percent. (Almost 20,000 Americans die each year using guns to commit suicide — a method that is much more successful than other forms of suicide.)