ABC News exclusive: Inside a cartel's human-smuggling operation

We are unlikely travelers on this dirt road, inching our way toward a tiny speck of a town in the middle of the northern Mexican desert.

The trail of dust from our tires kicks up in the midnight air, silhouetted by the full moon overhead, letting our contact know we're arriving as we approach a collection of houses.

It's a tense moment because although we've been invited to be here, this is cartel land. The threats are just about everywhere when there is this much money being made.

A small man in a black zip-up hoodie greets us and tells us to stay put for a bit, he needs to make sure it's OK we can keep going. He talks quickly into a walkie-talkie, the preferred way to communicate in the coded, you-never-know-who's-listening language of the smugglers.

Forty-five minutes later we're told to move ahead. The reasons for our trip to this place, around 100 of them, are gathered outside a cluster of houses a short ride away.

"They're from everywhere," the man in the hoodie tells us of the large group of people gathered, waiting expectantly. "It's like the United Nations."

Tonight, India, Nepal, Sri Lanka, Senegal and more are all represented. Other nights, it's Russia, Turkey, China. The list goes on.

They are all from different places but they are all migrants, sharing a singular purpose: to get to the U.S. And it's the men guarding them, the human smugglers with masks and guns, who will help them get there.

"Every week we're getting 200-300 people," one smuggler told ABC News. "But it's happening all over the border every day, every night."

A changing criminal landscape

The United States southwest border is in the midst of an unrelenting wave of migration.

Millions of people have arrived since 2021, numbers higher than ever before. The reasons behind those trips are varied and nuanced. Many are fleeing poverty or violence, political or religious persecution, wars, climate change. It's all here.

But what is often lost in telling that complicated story, is the how - how are millions of people are arriving so quickly, so efficiently?

That answer is simpler. It's organized crime.

"This amount of people arriving to the border would not be possible without this level of involvement by transnational organized crime," said Gerardo Rodríguez Sánchez Lara, an international security expert who has studied organized crime for decades.

Human smuggling is not new, but it has been transformed in the last few years into an industrial operation.

Cartels have quickly figured out that facilitating the flow of migrants to the U.S. border can be remarkably lucrative. Different organized crime groups control sections of the border, called plazas, with each controlling what happens inside its own territory.

In order to get to the border these days, migrants almost always have to pay.

"Everything has an owner and you need to respect that," one smuggler told ABC News. "[The migrants] can't cross by themselves. The only thing they would get is a certain death. They could give it a try but here, you have to pay."

Ruthlessly efficient and with a seemingly never-ending demand from people around the world trying to make it to the U.S., Rodríguez Sánchez Lara believes "human [smugglers] will be richer than drug traffickers within the next five years."

Manufacturing, transporting and selling drugs is remunerative, but difficult. Substantial investment must be made to produce the product. Sending it north and selling it in the U.S. comes with significant risk that the product, and therefore that initial investment, could be lost. No money is recouped by the cartels when authorities seize drugs.

With human smuggling, there is considerably less initial investment and risk. Migrants pay for their trips to the border up front. The smugglers bring them only as far as the wall, meaning they have to worry much less about U.S. authorities. And should the groups be intercepted by Mexican law enforcement and the migrants subsequently deported, the smugglers do not hand out refunds.

Compared to drug trafficking, human smuggling carries lower risk while the reward can be just as high, says Rodríguez Sanchez Lara. The money being made is astronomical.

ABC News saw a microcosm of that play out first-hand, when we were granted extraordinary access inside a human smuggling operation run by one of Mexico's largest cartels. This group is responsible for so-called "long haul" migrants - people that are often paying between $10,000 on the low end to $100,000 on the high end for a trip to the U.S.

Just after midnight, they huddled in a group around a smuggler with a cell phone, who was acting as a ticket checker of sorts.

To make the final push toward the border, all of the migrants had to pay a final fee to the cartel. While fees can vary, most paid the smugglers about $5,000 to get from Mexico City to the border, a payment in addition to whatever they had to spend to arrive at the capital city.

Once that payment was made, a photograph of the migrant was taken and sent to the smuggler on the ground, in what amounted to a digital receipt.

The smuggler scrolled through his list of photographs, matching pictures to the faces of the people standing in front of him. Once he matched a migrant's face with a photo, they were allowed to move forward. Those who hadn't yet paid were forced to wait.

To get an idea of how much money is being made every day in the human smuggling industry along the border, some simple math is required.

ABC News saw about 100 migrants that night in the desert. If each had paid only $10,000, the lowest estimated amount, that totals $1 million. That's $1 million dollars just from this one small group at this one part of the border.

These kinds of transactions are happening up and down the length of the border every single day. That is why the U.S. government estimates that the human smuggling industry is earning billions of dollars annually.

The money doesn't all go into cartel pockets but large amounts do, especially in Mexico. They have every incentive to continue pushing people north as quickly as possible, which often leads to migrants being seen not as people, but as commodities.

"It has to be worth it."

ABC News watched as dozens of migrants were packed into four stripped-down SUVs. Smugglers seated people with their knees to their chests, legs spread wide enough so that the next migrant could sit between their feet.

It is inhumane. It is also the most efficient way to cram as many people as possible into an SUV.

"I'm only asking God to make sure everything turns out well because we want to go [to the U.S.] to work and do things right," one migrant woman holding a child told ABC News. "It has to be worth it."

One migrant from Senegal told ABC News he spent his entire life's savings and went into debt to make the trip. "It's worth leaving Senegal to go to the United States because I will have a better life there," he said.

ABC News also saw two dozen men forced into a horse trailer, standing packed together so tightly that there was no room to turn around, let alone sit.

Each group of migrants was then driven three hours through the winding, bumpy desert until they reached a spot on the border wall through which they could walk. The trip usually takes two hours but there was a heavy law enforcement presence in the area that night so they had to take a longer route.

When they arrived, smugglers recorded each person crossing over and sent the videos to their bosses. It's proof of performance, showing they're doing their jobs.

"We're not taking advantage of them, we're doing what they ask us to do," one smuggler told ABC News. "There are others out there who do bad things to the migrants but we're not them."

ABC News' Anne Laurent contributed to this story.