Tijuana, Mexico—A few blocks from the US border, on a street corner in front of a large warehouse carved out and converted into a car wash, the locals say you can buy guns, watches, sex, meth—whatever. Conflicts and scuffles aren’t uncommon here, and in a bit of irony not lost on anyone, the cops are never far away. The municipal police keep a substation on the opposite corner, a constant line of nearly a dozen patrol cars across the street from the car wash and the open-air drug deals.

To set the scene in Tijuana, I could describe the manicured gardens outside the handsome midcentury city hall. I could take us to the Pacific Ocean, where artists and activists have turned the border wall, that scar of barbed wire and steel across the beach, into a series of beautiful murals. I could picture the engineers working in the city’s booming aerospace industry or the thriving restaurant scene, with the sweet tamales served after dinner, the craft breweries.

This corner, though, is where I learned Mexico has changed. One afternoon last October, I was interviewing a worker at the car wash when someone shouted to turn the room’s attention to the TV on the wall. We peered up at a news broadcast of scenes that looked as if they had come from a disaster movie. Masked men rode through the city in the back of a pickup truck, an enormous gun mounted on the tailgate. Then another masked man lying on his belly fired a high-caliber rifle into a group of scattering police officers.

“What is this?” I asked.

“It’s live. From Sinaloa,” someone answered, not looking away from the screen. “Culiacán. The narcos have gone to war.”

From that street corner in Tijuana, it was hard to understand what later became clear. After the Mexican military captured Ovidio Guzmán López—el hijo de El Chapo, the son of the infamous drug lord Joaquín “Chapo” Guzmán—the Sinaloa cartel sought his release by taking a hostage: the entire city of Culiacán. In a battle that lasted throughout the day, the cartel outorganized and outfought the military and police block by block. In the end, the government caved to the cartel. Guzmán was released in order to restore peace in the city. The narcos won.

On the corner, it was time to leave. The sun was setting as I traveled about five minutes to the main crossing between Tijuana and San Diego. On the Mexican side, Guardia Nacional members had been mobilized around the pedestrian crossing. I walked between two of these heavily armed troops to cross the bridge into the States. I passed rows upon rows of walls, fences, razor wire, and guarded gates. I showed my passport to an agent from Customs and Border Protection, who scrutinized my face as dozens of cameras recorded me. And then I was back in the US.

In recent years, resisting fear as a political impulse has meant resisting the argument that the United States needs this kind of security on the border—the surveillance, the barriers, the agents with guns. President Donald Trump’s dream, the wall, has been rightfully lambasted on the left as a useless monument to racist tribalism. Many see that the barrier’s intent is symbolic as much as tactical. The border, after all, is an imaginary line across the continent. A wall, however, could give it reality—a stone and steel way to separate supposedly good, honest Americans from the people on the other side, the people Trump calls “bad hombres.”

False security: The heavily guarded San Ysidro border crossing in Tijuana, Mexico. (Marco Ugarte / AP)

On days like October 17, when a cartel took an entire city hostage, it was hard not to feel a sense of relief as I crossed back into the US. I felt safer on the American side. What happened in Culiacán felt possible in Tijuana in a way it didn’t in San Diego.

The world changes in the space between San Diego and Tijuana. In recent years, the latter has become one of the homicide capitals of the world. In a city of 1.8 million people, more than 2,500 were killed in 2018 alone. Overwhelmed by bodies, the city’s morgue has overflowed. Neighbors protested the stench of decay, which regularly reaches their homes.

Just across the border, San Diego remains one of the safest big cities in the US. In 2018, with a population of 1.4 million people, it had just 86 killings—more than 95 percent lower than the homicide rate in Tijuana.

That massive difference in violence repeats along the entire border. Northern Mexico is now one of the deadliest places in the hemisphere. For US citizens, the State Department issued a Level 4 (“Do not travel”) advisory for Tamaulipas, a border state on the Gulf Coast south of Texas—the same level as for Syria, Yemen, and North Korea. At the same time, border cities across the southwestern US aren’t just safer than their Mexican counterparts; they’re also some of the safest places in the country. Laredo and Brownsville, two towns just across the border from Tamaulipas, are both listed among the safest cities in the United States.

A wave of violence: Mexican soldiers guard a site where a man was killed by gunfire in Tijuana. (Guillermo Arias / AFP via Getty Images)

As the rates of violence increase rapidly in Mexico’s border towns, some have been surprised that there’s essentially no spillover violence in US cities. Could this be the effect of a militarized border? In between San Diego and Tijuana, a 14-mile steel barrier carves through the landscape. At times such as the day of the Culiacán battle and when I’ve heard gunshots while out reporting, it can feel as if those miles of concertina wire and armed patrols are justified—that as Trump and his allies argue, we need a strong barrier to stop the violence that plagues Mexico from migrating into this country.

That’s not the truth. There’s a simple fact that the wall obscures: The people in Tijuana are not the true source of the violence in that city. And keeping certain people out is not actually what keeps San Diego safe.

When I drove to Tijuana, I crossed a border where the crime rate changed staggeringly, well before I even made it to Mexico. In Los Angeles, I headed toward the coast down Highway 110. In just 20 minutes, I went from Manchester Square (between Compton and Lawndale) to Rolling Hills Estates, a Malibu-like neighborhood in the hills northwest of Long Beach. In those few miles, the per capita violent crime rate plummeted 98 percent—from about 85 incidents per 10,000 people to just 1.2 incidents.

There are no border walls between Rolling Hills and Manchester Square, no checkpoints, no patrols keeping people out. Yet the violence stays incredibly localized; you can measure relative security by zip code. There are similar borders all over the country, in Chicago and New York, St. Louis and Miami, Houston and New Orleans.

How does this happen? For researchers studying violence, trying to understand why a city like Tijuana has become violent can look similar to trying to understand why the people of Flint, Michigan, began feeling sick in 2014. It’s not really a question of who the people are. It’s a question of where they live.

From news reports in the United States, the growing violence in Mexico can seem a straightforward, bloody battle between the narcos and government agents (who are also sometimes narcos). However, for people such as Iván Cruz, who has lived most of his life in Tijuana, the growing danger doesn’t feel like a war zone’s. It’s something different.

Cruz lives in Camino Verde, a southern Tijuana neighborhood that’s notoriously dangerous. In the past few years, he’s watched violence spread through his city like an epidemic. (As recently as 2014, Tijuana had fewer than 500 homicides per year. Last year nearly 2,200 were killed, a more than threefold increase.) While Americans focus on narco shootouts with high-powered weapons, Cruz hasn’t seen the cartels swoop in and claim territory. Rather, it’s the people of his neighborhood who seem to have changed. A toxic fog of danger and distrust now hangs in the air. People are killing each other. Neighbors are dying, and often no one knows who killed them. In this atmosphere of intense fear, people who were once peaceful feel forced to defend themselves; they pick up guns or join gangs. This is no war. There are no clear sides or enemies, no bad guys and good guys. Instead, it feels like the arrival of a plague, some disease that can spread through a neighborhood and take lives.

“It can touch you wherever you are,” Cruz said. “You can try to stay out of bad areas, you can stay at home with the doors locked…but the violence can touch you anywhere.”

Increasing militarization: The US pours billions of dollars into border security each year. (Marco Ugarte / AP)

The first step toward understanding the epidemic of homicide in Tijuana is realizing that the word “epidemic” isn’t a metaphor. About 40 years ago, researchers at the Centers for Disease Control in the United States began a series of odd experiments. By that time, modern epidemiology had essentially eradicated diseases like tuberculosis and influenza, which previously were significant sources of death and misery for Americans. Seeking to rededicate resources in December 1980, a group of CDC epidemiologists turned their attention to homicide, another common cause of untimely death. The scientists ran an experiment that was in many ways a shot in the dark. They began tracking instances of unsolved child disappearances and murders in Georgia. As they gathered more data, they saw the outlines of what later scientific work would make clear: Violence seemed to spread like a contagious disease.

“The No. 1 predictor of whether a person will go on to commit violence, more than anything else, is if that person has been exposed to violence in the past,” said Charlie Ransford, the director of science and policy for Cure Violence, a US-based organization that uses epidemiological models to stop the spread of violence.

Right now, Mexico is experiencing its highest homicide rate in modern history. More than 120,000 people have been killed since 2016 (more than all US deaths in World War I). Recently, Americans’ attention to the violence spiked after nine people—members of the Mormon-affiliated Lebáron and Langford families—were massacred in northern Mexico last November. But during much of that year, almost 100 people were killed in Mexico every day.

In my conversations with Cruz and others in Tijuana, the country’s most murderous city, it soon became clear that it’s not just a problem of narcos or soldiers. People talk about the violence as if it were a living force, something that’s come to the city and affected people, something that can touch you and go into your house.

Thinking of violence as a disease, then, makes a lot of sense. An epidemiological model of violence can explain why the homicide rate in Mexico has grown exponentially. Violence isn’t caused only by “bad guys” who can be arrested and locked up. It’s caused by cycles of risk and exposure, like any disease. People who were once healthy and peaceful can become sick with violence.

“It makes absolutely no sense if you think about it rationally—that a person experiences the harm of violence and then goes on and does it to other people,” Ransford said. “But when you understand it as a contagion, something that is being passed on from exposure, then it starts to make sense.”

Like many researchers studying violence, Ransford is now using a public health approach to flatten the curve. The same way that doctors educate the public about contagion risks or distribute condoms to help prevent the spread of sexually transmitted diseases, organizations like Cure Violence use targeted interventions for people affected by violence (for instance, someone who saw a friend shot), including connecting them to social workers, mediators, and therapists. The model has been astonishingly successful. In Cure Violence’s first year working in one of Chicago’s deadliest neighborhoods, the number of shootings went down by more than 67 percent. That success has been repeated in 20 cities across the United States, as well as in El Salvador, Honduras, Syria, Iraq, and other countries. (During the Covid-19 pandemic, Cure Violence has retrained its staff to encourage public health practices that discourage the spread of both the virus and violence.)

When I asked Ransford why violence seems to spread so much more easily through a city like Tijuana than San Diego, he replied, “Think of how a disease spreads. The biggest factor is the contagion itself, but there are other cofactors of transmission.” He used cholera as an example, which typically needs a water source to spread. In San Diego, if someone caught cholera abroad and brought it home, it wouldn’t cause an epidemic. San Diego has a working sewage system and clean tap water. But in areas without sewage systems or where the same river is used for drinking water and waste disposal, a single person with cholera can infect an entire city. This describes the difference between the two cities: There are established institutions that work in San Diego but don’t in Tijuana, and there are vectors of transmission in Tijuana that don’t exist in San Diego. So even when the contagion crosses the border—and the existence of tunnels and smuggling routes is an open secret in both cities—it doesn’t have the same danger of spreading in California as it does in Mexico.

Asked whether the border wall could be keeping the violence in Tijuana from crossing into the United States, Ransford conceded that it might have an effect. But the more important variables, he said, are the environmental differences that make one city a hotbed for violence and the other a safe zone.

“What are the vectors of transmission in a place like Tijuana?” he asked. To put it another way, what is the violence equivalent of a contaminated river?

Camino Verde: Rapidly and haphazardly urbanized, the poor neighborhood is one of Tijuana’s most dangerous.

Iván Cruz’s neighborhood in Tijuana, Camino Verde, is appropriately named. In its center, a canyon road curls along a creek bed, through the pale green of the Baja California brushland. In the late afternoon, the valley cools as the sun sinks behind the coastal mountains; the shadows of the scraggly trees lengthen along the steep hillsides, where houses made of fiberboard and tin roofs are stacked one on top of another. Like many neighborhoods on Tijuana’s outskirts, Camino Verde was rapidly and haphazardly urbanized. The roads are winding and poorly maintained, and the electricity and sewage systems are improvised. Stray dogs, the real kings of the roads, stop traffic, and feral chickens wander between houses.

While Camino Verde has a reputation as one of Tijuana’s poorest and most dangerous neighborhoods, its true notoriety comes from a small number of its residents. According to locals, it’s known as the birthplace of some of Mexico’s most famous killers. Taking advantage of the desperate conditions and lack of opportunity in the neighborhood, the cartels have long gone there to recruit their most brutal sicarios.

Up on one of the hills of Camino Verde, along a perilously steep walkway, Cruz lives with his parents, his sister, her son, his widowed sister-in-law, and her young son in a tidy house. When I first visited him, one of the neighborhood’s stray dogs barked at me playfully as a man watched us closely from a car parked across the street. (Halcones, or gang lookouts, are a fixture in the neighborhood.)

Cruz was dressed in a neat blue polo shirt and carried a small backpack. At 30 years old, he has a round, boyish face and a fastidiously maintained haircut. He told me how he studied communications at a local university and graduated to work in a human resources department at one of the city’s many factories. (“Finances and management,” he said proudly.)

“When my family moved here in ’97, Tijuana wasn’t known for violence. But it’s increased so much since then, to the point that now one is afraid to go out into the street. You don’t know if someone will stop you, assault you, take your money.” Cruz said that his family tried to adapt to the growing insecurity. “At first, you just think, ‘OK, I’m going to be more careful.’ You tell yourself, ‘I’ll stay safe. I’ll teach my kids what’s good and what’s bad.’ But then something happens to your family.”

When Cruz invited me into his home, I noticed a small shrine above the crib where his nephew sleeps. On a makeshift cardboard shelf, paper flowers lay next to a printed photo of a young man, Cruz’s brother, Alejandro. In November 2017, Alejandro (a pseudonym) became one of the thousands killed in the new wave of violence. Neighbors found his body not far from Cruz’s house, at the bottom of the hill on the road that runs along the green creek bed. He had been shot twice.

In great detail Cruz told the story of learning that his brother had died but said there’s still so much he didn’t understand. He knew his brother, depressed and struggling under the insecurity of life in Camino Verde, sometimes used drugs; he also knew the corner where they found his body is near a now derelict liquor store where the rumor was you could buy more than just alcohol. However, even today, Cruz doesn’t know exactly what happened to his brother. The police, if they ever truly investigated, have given up, despite the family’s constant pleading for more information.

“We don’t know anything about what happened. We have no idea—nothing,” Cruz said. “But if there wasn’t earthly justice, we hope there will be divine justice. We are believers.”

The continuing mystery of Alejandro’s death illuminates the specific nature of the violence in Tijuana and the rest of Mexico. The vast majority of homicides in Tijuana—more than 90 percent—go unsolved. And the killings that do get prosecuted are rarely the ones that take place in areas like Camino Verde. There’s a reliable sense among residents that the crimes that actually get investigated are the ones that happen in wealthier neighborhoods, where the police and other municipal resources are concentrated. In contrast, in places like Camino Verde, there is an understanding, terrifying and bleak, that a person can kill someone else without consequence.

This, perhaps more than any other factor, is the equivalent of that contaminated river: impunity. In Tijuana, you can kill without consequence in a way that’s not possible in a place like San Diego. Tijuana’s broken criminal justice system is similar to a broken sewer system. It foments the contagion of violence and helps it spread rapidly through the population.

Impunity has been a documented cofactor of violence in cities like Chicago and Los Angeles, where police often fail to properly investigate gang-related killings; in Chicago, police solve only one out of every 20 shootings. Impunity can also explain much of the violence in the rest of Mexico. According to a 2017 study from the Mexican-based Center for Studies on Impunity and Justice, the country had the fourth-highest rate of impunity worldwide. As recently as 2016, it was estimated that fewer than 1 percent of crimes in Mexico were punished. The impunity tends to be worse in the states most affected by drug-related corruption: the border states of Baja California and Tamaulipas, as well as agricultural areas such as Guerrero and Oaxaca.

“Tijuana, with California just across the border, is one of the most important trafficking points,” said Tijuana Mayor Arturo González Cruz (no relation to Iván Cruz). “This has created a very serious problem for us.” After decades of narcos carving out a transit channel through Tijuana, the city’s justice system has been seriously compromised. Many residents consider the police corrupt and unreliable, and they’re often proved right. This means that Cruz’s story is by no means rare. Hundreds of families live with a suddenly empty bed in their house and a deep sense of the unknown.

After Alejandro’s killing, Cruz walked the streets wondering if any of the people around him had killed his brother and why. Without anything like the rule of law, his family members lived in fear and had to learn to navigate a complicated web of self-defense. They worried that Alejandro might have been targeted and that they too might be marked. They began avoiding certain streets, going home before nightfall, and doing everything they could to keep a low profile. They didn’t want to make trouble. Then a year later, as they planned a memorial for Alejandro’s death, tragedy befell the family again. Cruz’s cousin was shot and killed.

“At that point, we fell into a state of total panic,” he told me. “We all gathered in the house and locked every door. They had us terrified. We were scared to even go to the corner shop to get tortillas.”

In this atmosphere of terror, the cartels find Camino Verde ripe for recruits. Without the police to protect them, residents have to defend themselves as best they can. It is to people living in this state of fear—in true, constant danger—that the narcos make their offer: We will put a gun in your hand. We will make you a killer, invincible. You can stop being afraid.

Cruz had remarkable patience when we talked about the origins of the violence that claimed his brother. When I asked why he thought the homicide rate was so different between Tijuana and San Diego, he appealed to sociology rather than demonize any of the people in his neighborhood. “The economic pressure—the need to eat—is stronger in Tijuana than San Diego,” he said.

Along with the language and the homicide rate, there’s another major characteristic that changes when one crosses the border from San Diego into Tijuana: the poverty rate. In Tijuana a high percentage of the city’s residents are college educated, and the unemployment rate is low. But in a city sharply stratified between wealth and precarity, violence has defined borders, even without any walls. While the deeply marginalized outskirts of the city suffer from shocking rates of crime, much of Tijuana remains perfectly safe. The city is still a popular tourist destination, despite being one of the world’s homicide capitals. The microbreweries, beach cabanas, and casinos frequented by tourists have remained secure. When you map the city’s homicides, you see the majority of them have occurred in Tijuana’s southern and especially eastern additions, far from the wealthy beachside and downtown areas.

When I asked González why people turn to violence in his city, he sighed and leaned forward in his chair. “Listen, if you do not have the ability to make a living to support your family and there’s an easy deal available and that deal is drug trafficking, then you’re going to get into that deal,” he said. “But if you have a good job that allows you to support your family honestly, to take care of them better, then there won’t be the pressure to think of work on the other side.”

While drug trafficking continues to affect the city, the crime in Tijuana today looks much different than it did in the late 2000s, when rival cartels battled it out in the streets. The fighting between the powerful narcos has largely died down, quite possibly because of a consolidation of control. Now the violence largely stems from something else. Tijuana is in the midst of a serious addiction crisis. Cristal, meth, has flooded the streets. Just as the opioid epidemic played out in economically blighted areas in the American heartland, so drug use skyrocketed in Tijuana as jobs and economic security cratered in the late 2000s. Today many of the homicides are targeted violence on a lower level, as street dealers fight to maintain control of their corners.

Experts like Ransford hope that we can come to see violence in the same way we’re learning to see addiction. Instead of viewing it as a moral failing on the part of the addict, we’ve begun to understand it as a disease—and also as a symptom of a society’s failure to provide jobs, community, and meaning. “When a person has been behaving violently, we believe deeply that that individual is having a health problem,” Ransford said, “that they almost always have a history of exposure to violence in their lives.”

In many ways, it’s a disturbing reality to come to terms with: that violence is something universal to humanity. We all have the capacity to commit violence, and it’s simply a question of the pressures that drive us to do so.

For many Americans, it’s more comforting to think of the horrific violence playing out in Mexico as something essentially Mexican, something we can keep out with a border wall. However, any neighborhood in the United States could fall into the same perils if afflicted by the same social pressures. Indeed, many have.

If you follow the green road up the hill through the center of Camino Verde, past all the tin-roofed houses, a white, hypermodern building suddenly appears along the creek bed. Casa de las Ideas looks like a collection of clean white cubes and square portals. Out front, there’s a small sculpture garden in a cobblestone patio. Behind the building, there’s the half moon of an outdoor amphitheater.

Casa de las Ideas is a digital library opened in 2013 as part of an urban development effort in the neighborhood. Today it works like a community center for Camino Verde’s youth. Every day, the library hosts educational and artistic programming for children and young adults.

Inside, Christian Zúñiga, an art professor from the Autonomous University of Baja California, explains that this work is a direct defense against the gangs that seek recruits in the neighborhood. “This is primary prevention,” he said. “The pressure to engage in [criminal activity] begins early.” The boys are recruited when they’re still in primary school. “We try to establish different horizons. We try to change attitudes and predispositions by offering people new opportunities.”

The idea behind the community center is that violence can be prevented, in part by connecting at-risk youth with education, career planning, and a safe place. (In addition to its attractive modernist design, the building’s semibrutalist facade is as thick as a bunker.) Casa’s mission has some similarities with Cure Violence’s model. Instead of addressing violence by criminalizing local residents, it seeks to connect them with resources and opportunities.

At Casa de las Ideas, there’s an understanding that the world can’t be split into good people and bad guys. In a healthy, secure neighborhood, safety prevails; in a marginalized, exploited neighborhood, violence spreads like a disease. Anyone thrown into the dangers of a place like Camino Verde might pick up a gun. But the same people the cartels hope to recruit could become doctors or artists if placed in a different environment. Casa de las Ideas tries to create that environment.

When I asked Zúñiga for his ideas about the origins of “Mexican violence,” he bristled at my phrase. “The weapons [the cartels] are using come from the United States, and people in the United States are [the ones] who buy the drugs,” he said.

The United States is a world leader in drug consumption, and the clear majority of the guns in Mexico come from the US. So while the violence may play out south of the border, in many ways Zúñiga is right: It’s not just Mexican violence; it’s also American violence, killing Mexican people.

On a fall afternoon, Cruz met me at Casa de las Ideas. We spent some time admiring the architecture, then we drove along the riverbank. Along the way, we passed a variety of recently constructed facilities—a soccer field and playground, another community center, a tidy park.

“I think it’s wonderful there are opportunities coming into the neighborhood,” Cruz said. He credited being able to attend college as the reason he didn’t fall into crime. He had other opportunities, other horizons.

As we drove along the dusty bank, he suddenly said, “Stop right here. This is the place.”

We got out of the car in front of a building with a rundown facade painted an almost neon blue. It was the liquor store. “This is where they found his body,” Cruz told me.

Quietly, we looked around. I wondered what it was like for him to be there now. Not just where they found Alejandro’s body but in the same neighborhood where he was killed—the same neighborhood that killed him.

Cruz said that, at a certain point, he and his family gave up living in fear. Trying their best to stay safe, confining themselves to the house, felt like living in a prison.

“One gets tired of living with that fear. You decide, ‘I’m just going to try to live a normal life.’ You go outside again,” he said.