Don Winslow is the author of 19 books, including New York Times best-sellers and the recently published " The Cartel ." He won the Raymond Chandler Award in 2012. The opinions expressed in this commentary are his.

(CNN) I've been writing about the war on drugs for 15 years.

That's a sad statement, if you think about it.

Particularly given that 15 years is less than half the life of this particular war , which, at 44, has gone on longer than the Civil War, World War II, Vietnam and Afghanistan combined.

The war has multiple fronts, but my particular beat is the Mexican border, across which the vast majority of illegal drugs now come into the United States. I've gone out with the Border Patrol, walked the line, sat in cars observing the crossing under the hostile gaze of cartel gunmen on the other side. I've talked with DEA agents, cops, drugs users, and yes, drug traffickers.

Fifteen years on the border observing the war on drugs.

Cocaine, heroin and meth pour across -- mostly carried in trucks, but also hidden in cars, lugged on foot by human "mules," walked across taped to people's bodies, hidden inside corpses, packed across on actual mules or horses (two of which, abandoned in the desert, lived out their lives on our place), run through tunnels, launched by catapults -- any method that human ingenuity can devise.

You know what drug isn't coming across in such great volume any more?

Marijuana.

Seizures of marijuana at the border are down almost 40% since several states in the U.S. have legalized it, The Washington Post reported . Mexican marijuana traffickers will tell you that it's not worth it anymore -- they can't compete with the domestic American price and quality. The wholesale price of Mexican marijuana has dropped from $100 a kilogram to $25. Growers in Durango and Sinaloa have stopped planting the crop.

We've cut marijuana imports almost in half within the last two years by legalizing it... Don Winslow

So we're winning the war on marijuana along the border -- costing the violent sociopaths of the cartels millions of dollars -- by legalizing it.

That's the good news.

The bad news is that the cartels have responded to this loss by shipping more coke, meth and especially heroin. The heroin epidemic in the Northeast is mostly supplied by the Sinaloa cartel, by far the dominant drug trafficking organization in Mexico today. Addicts who were using prescription opiates are turning to Mexican heroin because it's cheaper.

Cheaper -- at $40,000 to $50,000 a kilo by the time it hits, say, New York City.

A kilo of raw opium sap produced in Mexico costs about $1,500. That's $1,500 on one side of the border, $50,000 on the other. That's a pretty good profit margin. A kilogram of cocaine costs about $12,000 to buy in Mexico but is worth $27,000 once it crosses that border.

So after four decades of the war on drugs, we've cut marijuana imports almost in half within the last two years by legalizing it, while the heroin, coke and meth just keep coming.

In essence, when we stop fighting, we win.

When we keep fighting, the cartels win.

When the drug bosses look at the border, they don't see fences or walls -- they see money.

The border is siempre verde -- always green -- to drug traffickers.

They've told me so. They love that border fence more than the most right-wing militia member riding around the desert on an all-terrain vehicle does. That fence, that wall, those customs agents are worth billions to them.

You might ask what difference it makes whether the cartels sell the drugs or Americans sell the drugs.

We still have the drug problem, right?

Right.

But maybe another 100,000 people in Mexico wouldn't be killed in drug-related violence, as they have over the past ten years.

We're so focused on terrorists halfway across the world that we've barely noticed the human catastrophe that's happened just across our border in one of the bloodiest conflicts in the Western hemisphere since the American Civil War.

You want to talk about terrorism?

The cartels routinely torture and slaughter, they put their decapitations out on video clips. (ISIS has only ripped a page from the cartel playbook.) They've depopulated entire villages, co-opted police and government. They're now heavily involved in human trafficking, with a twist -- they kidnap immigrant families, force the husband or a brother to mule drugs across the border by threatening to kill the family, and then often kill them anyway.

That's terrorism.

One of our presidential candidates recently said, speaking about immigration, that Mexico doesn't send us its best. Shame. I know quite a few of the "undocumented" who have come over, and they are some of the finest, hardest-working good family people that I have ever known. I'm proud to have them as neighbors.

But because their immigration was illegal, the cartels profit from them, just as they do the drugs.

Because the cartels control the profitable border territory.

Because drugs are illegal.

At least 37 people were killed in a gunfight May 22 in Mexico, one of the drug war's bloodiest clashes.

I'm not just blaming prohibition. Addiction is one thing, but recreational drug users in this country have to take responsibility for what they do. It always boggles my mind that people will be so particular about only buying fair-trade coffee or free-range chicken, but will think nothing of doing coke or weed that was transported or grown by slave labor forced to work in the fields by the cartels, women who are often raped and turned to prostitution.

I don't want to harsh your high, but consider the probability that your buzz comes to you with blood all over it.

From a sadistic cartel.

After 15 years of writing about them, chronicling their horrors, seeing their damn video clips and photos, sitting with the loved ones of their victims, I'd like to put those cartels out of business.

They're not so interested in marijuana now because there's not as much money in it. Why don't we take meth, coke and heroin away from them, too?

The war on drugs isn't working.

As long as we wage it, the border will be a bloody battleground.

Stop America's longest war.

We can't afford another year, never mind another 15.