A Border Patrol agent walks near the secondary fence separating Tijuana, Mexico, background, and San Diego. (Gregory Bull/AP)
Mary E. Mendoza is assistant professor of history and Latinx studies at Penn State University and the David J. Weber Fellow for Study of Southwestern America at the Clements Center for Southwest Studies at Southern Methodist University.

As immigration policy again dominates the news, President Trump’s administration has resorted to creative justifications for its draconian policies, including demands for a border wall. Interior Secretary Ryan Zinke might just have trotted out the most creative rationale, arguing: “It’s a national security issue, a national defense issue, it’s a humanitarian crisis, and oh, by the way, it’s an environmental crisis,” implying that a wall would help solve all of these problems.

Perhaps Zinke is right about the broad dimensions of the problem. But instead of solving the environmental and humanitarian crises at the border, a wall would exacerbate them. Walls don’t stop migration. Instead they push migrants to navigate more dangerous landscapes where they risk their lives while doing grave environmental harm.

The United States has been building border fences along the U.S.-Mexico boundary since 1911. But for the first three decades, these fences were not meant to control human migration. Instead, the United States Department of Agriculture (USDA) constructed them to combat a cattle disease that ravaged the northern ranges of the United States. A tick that moved from south to north was the culprit of this fatal disease. Cattle in the south had been exposed to the tick before the age of 6 months, so they were immune to the disease. But when those cattle traveled north, they exposed susceptible cattle to the bug.

After launching a successful campaign to rid the United States of the tick, USDA officials realized that cattle crossing the border might reintroduce the pest, so they built fences to funnel cattle through ports of entry where the animals could be inspected and treated. In the decades that followed, outbreaks of the highly contagious foot-and-mouth disease, which spreads rapidly among cloven-hoofed animals, prompted the USDA and the National Park Service to build even more fences to stop cattle from wandering across the international boundary.

During this time, Mexican people were more or less welcome to cross the border for work. In fact, during World War II, the United States and Mexico worked together to transport Mexican workers into the United States to help fill labor gaps. This program, later dubbed the Bracero Program, was such a boon to the agricultural industry that it extended well beyond the end of the war, ultimately lasting until 1964.

Not all Mexicans qualified for the program, though, and many simply crossed the border on their own, hoping to find work. This effectively created what we now call undocumented or unauthorized migration. Unsanctioned migration caused problems on both sides of the border, depressing wages for Braceros in the United States and depleting the workforce in Mexico. As a result, as historian Kelly Lytle Hernandez has explained, both nations set out to monitor and regulate it.

Beginning in the late 1940s, the fences that had been used to control cattle migration morphed into tools to alter the nature of human migration. By supplementing cattle fences with new, chain-link fences in urban areas, Border Patrol agents hoped to funnel migrants away from populated areas along the border where they could blend in, to more isolated areas where they could be spotted and apprehended more easily.

This change marked a crucial transitional moment in border fence history. With increasing unauthorized entry, the focus shifted from animals to people.

This effort, supported by both parties, meant that for more than half a century, the fences grew in length and height and covered more and more area. All of these fences pushed migrants into deserts, across rivers and over mountains where many have lost their lives. Each phase of fence construction has also come with intermittent increases in the number of border agents, making the borderland an increasingly militarized zone.

For all of this time, effort and cost, the payoff has been decidedly mixed. No fence on the southern border — for animals or for people — has ever fully worked. Fences meant to control the spread of cattle ticks did not entirely stop ticks from crossing the border. In the 1950s, Texas experienced a new outbreak of the disease, well after the first fences built to stop ticks were constructed. Today, the USDA still deploys “tick riders” — agents who ride on horseback along the U.S.-Mexico border in search of wandering cattle.

Foot-and-mouth disease remains a realistic risk, as well. The disease is so potent that it could travel across the border through the air or sneak in on the shoe of a U.S. citizen who has traveled to a place where the virus is endemic. With increased air travel, the risk of the disease entering the country has likewise ballooned. The best protection is actually not a fence or a wall but, rather, a pack of beagles employed by the USDA to sniff our bags and our clothes in search of contraband that could reintroduce the virus to the U.S. mainland.

People continue to cross the border in large numbers, as well. Tunnels, ladders, aircraft, bolt cutters, hiking around existing fences and good old-fashioned climbing have all granted unauthorized entry into the United States.

Fences have not worked to stop the migration of bugs, viruses or people, and a wall won’t either.

Moreover, Zinke’s suggestion that such barriers would be good for conservation is also wrong. These fences — built to contain animals and then humans — have damaged and destroyed their environs.

Fences near Organ Pipe national monument, for instance, were among those constructed to stop cattle from crossing in the 1940s. Today they are taller and longer and meant to keep people out, but their environmental impact remains the same: severing habitats for critical flora and fauna. The Border Patrol roads that surround them do the same.

Recently, Border Patrol roads have proved dangerous for people, as well. And as fences extend the time it takes for migrants to cross the boundary line, foot trails create new paths for runoff water and also put flora and fauna at risk. Longer journeys also mean that migrants must carry increasing amounts of provisions with them to survive, which ultimately means that there is more garbage left in the desert, or worse, bodies and their possessions decaying in the punishing sun.

As more fences have gone up, deaths in the desert have increased dramatically. In the decade after the Secure Fence Act of 2006, which called for 700 miles of reinforced fences in the most highly trafficked areas along the border, the death rate rose to five times the amount accounted for in the decade that preceded it.

This situation is both an environmental crisis and a humanitarian one, but it is because of fences and walls that those problems exist. In the name of deterrence, Americans have adopted increasingly exclusionary immigration policies and built bigger fences. But instead of deterring migrants, they have simply made passage riskier and led to environmental damage. And the cruel way with which the Trump administration has carried out these long-standing policies is simply exacerbating the problem.

If Trump is right about anything, it’s that Mexicans and Central Americans are paying for these policies — with their health, with their lives and now with the well-being of their innocent children. But Americans are paying for them, too, in the immeasurable damage done to the rich and diverse ecosystems of the U.S.-Mexico borderlands, in the tearing apart of families that traverse the border and in our deteriorating international reputation.