Let’s say you were writing a novel about a homicide. You’d want to describe the killer’s neighborhood and family background. You’d want to describe his school, his culture and his gang.

You’d want to describe how he got into crime, his prior arrests, his prison time, his drug use and his relationship with his probation officer. You’d want to describe how he got the murder weapon, what police presence there was the night of the killing.

In other words you’d want to describe a long killing chain, a complex series of links leading up to the event.

Over the last 25 years, American authorities have tried to interrupt that killing chain at almost every link except one. There have been vast changes in proactive policing, mentoring programs, gang eradication programs, incarceration rates, cultural attitudes and so on. The only step in the killing chain that we haven’t touched is gun acquisition. Federal gun control laws have become more permissive over the last several years.

This de facto approach — influencing the whole killing chain except gun acquisition — has nonetheless contributed to a phenomenal decline in violence. Murder rates overall have fallen about 50 percent, to levels not seen since the Kennedy administration. Thousands of people are alive today because homicide rates dropped so precipitously.

Now we are in the middle of another debate about violence. If we lived in a purely rational society, this debate would have started with a series of questions:

What explains the tremendous drop in violence?

How can we build on recent efforts to bring the murder rate even lower?

These questions would have led to a series of more specific questions about police procedures, probably the most direct way to prevent shootings.

For example, as Heather Mac Donald of City Journal, published by the Manhattan Institute, points out, 75 percent of the shootings in Boston over the past 30 years have occurred in 4.5 percent of its area, while 88.5 percent of the city’s street segments had not had a single shooting. So how can we focus police resources on those few areas that host most of the killing?

Or as Robert Maranto of the University of Arkansas points out, New York police chiefs and precinct leaders are held accountable for changes in the murder rate in their areas. New York has seen an 80 percent drop in the homicide rate. Why aren’t police officials held similarly accountable in other cities?

But those questions are rarely asked. Instead, the national debate has focused on just one link in the killing chain: acquisition of the gun.

Now I understand why the gun has taken center stage. The gun is the shocking fact at the moment of the murder. Also, in any moral question or frightening conflict, there are a lot of people who are uncomfortable with the human element and like to fixate on the material factor.

The sad fact is that gun acquisition is probably the link on the killing chain least amenable to influence. We live in a country that already has something like 250 million guns. It’s hard retroactively to get a grip on them.

Past efforts to control guns have not dramatically reduced violence. The Gun Control Act of 1968, the Brady Act of 1993 and the Assault Weapons Ban of 1994 all failed to reduce homicides significantly. The Brady law, for example, led to a drop in suicides for those 55 and older, but a 2000 study commissioned by the American Medical Association found that it did not lead to a reduction in the murder rate.

Other studies have found more significant effects, but nothing like the impact we’ve seen from changing police procedures and other efforts up and down the killing chain.

If we could start the violence debate over, I’d begin with universal background checks. Acknowledge that on their own, these checks won’t accomplish much. (Drug dealers from Baltimore are not driving to West Virginia gun shows to acquire weaponry.) But use those checks as the first step in a series of policies to reinforce gun trafficking laws and reassert police control over the zones of concentrated violence.

We have a successful history of reducing violence by spreading efforts across the killing chain. We have a disappointing history of trying to reduce violence with a gunobsessed approach. Let’s focus on what works.

DAVID BROOKS writes for The New York Times News Service.