About 30 armed Border Patrol agents swarmed a small camp in a remote part of the Arizona desert last Thursday. From the intensity of the raid, you might think they were hitting a drug smuggling depot.

Instead, it was a humanitarian relief station run by the nonprofit No More Deaths. There volunteers provide water and urgent medical services to migrants crossing the inhospitable region.

Thursday's raid, in which four migrants were arrested, didn't just represent an escalation of interference with No More Deaths' work. It's part of a growing securitization of the southern border, a crackdown that is compelling immigrants to take increasingly hazardous and remote desert routes into the United States.

At the beginning of the 21st century, the country's border security infrastructure was much smaller: The 1,954-mile frontier between the U.S. and Mexico had a mere 60 miles of fencing and about 8,500 immigratrion officials patrolling it. After 9/11, the border fence stretched to 700 miles and the number of border patrol agents exploded to over 17,000 stationed in the Southwest alone. The border also became a surveillance state, with 8,000 cameras, 11,000 motion sensors, and even drones watching out for unwanted immigrants.

As Cato policy analyst David Bier pointed out in a recent Reason feature, "one byproduct of making it harder to enter is that people will choose to cross in increasingly dangerous points along the border." In 2000, the U.S. government arrested 1,643,679 illegal immigrants attempting to cross the southern border; at least 380 migrants died making the crossing. Last year, Border Patrol agents apprehended only 408,000 people for entering the country illegally, but the number of reported dead stayed roughly the same, at 322.

In other words, in 2000 one migrant died on the U.S.'s southern border for every 4,325 migrants detained by the Border Patrol. In 2016, the ratio was one dead migrant for every 1,269 apprehended alive.

The Office of the Medical Examiner in Pima County, Arizona—where the No More Deaths raid took place—recovers the remains of dead immigrants once every two to three days. The overwhelming cause of death is exposure to extreme temperatures and dehydration. Since 2000, 6,700 migrants have died in this way while traversing the American Southwest.

No More Deaths was established to bring that number down to zero. For the past 13 years they have been operating a desert outpost in Arivaca, Arizona. From there volunteers carry water to remote foot trails known to be used by immigrants. Throughout that time, immigration officials have reportedly harassed the group. Volunteers have been charged with littering for leaving full jugs of water in the desert. Border patrol agents have also been caught on film pouring water jugs onto the ground.

In 2013, however, the group reached an agreement with the Tucson branch of Border Patrol: The government would not interfere with the organization's medical and humanitarian work. That agreement was supposedly affirmed just two months ago. No More Deaths has released a statement calling last Thursday's raid a violation of that agreement, saying it "has deterred people from accessing critical humanitarian assistance in this period of hot and deadly weather."

"People crossing the deadly and remote regions of the US–Mexico border," the statement added, "often avoid seeking urgent medical care for fear of deportation and incarceration." Being allowed to provide that care in a safe environment was crucial to that work. But with raids like this—and with the Trump administration escalating immigration arrests and looking to hire another 15,000 Border Patrol agents—that lifesaving help may become far more difficult.