Expert Commentary

What the research says about border walls

This roundup of research focuses on border barriers — what they are, why they have become popular, whether they actually help countries control their borders and how they impact the environment and local communities.

Vehicle stuck on top of a border barrier.
(U.S. Customs and Border Protection)

As American lawmakers argue over whether to fund a wall along the United States’ southwestern border, the federal government has moved ahead with plans to replace some of the fencing it built there years ago with a 30-foot-tall steel bollard wall. Meanwhile, a growing number of countries worldwide have built border walls and other barriers to try to control the flow of people and goods.

There are a total of about 70 border barriers worldwide, Elisabeth Vallet, director of the Center for Geopolitical Studies at the University of Quebec-Montreal, told Journalist’s Resource. Her research demonstrates how popular these structures have become — there were about 15 of them in 1990. Vallet is one of a number of scholars in the field who have spoken out against man-made barriers, arguing they are expensive and dangerous and questioning their effectiveness. Several of those scholars weighed in with essays published in a recent issue of the Journal of Latin American Geography.

Here in the U.S., the Department of Homeland Security (DHS) has erected more than 650 miles of fence and other types of barrier along the almost 2,000-mile U.S.-Mexico border. Even before President Donald Trump took office, federal law required the barrier to be expanded by another almost 50 miles. In December, DHS announced that it had completed most of a $292 million project to build 40 miles of steel wall to replace “an outdated and operationally ineffective barrier” in the San Diego, El Centro and El Paso sectors of the border.

Lawmakers have until Feb. 15 to reach a compromise on a new border security plan or there could be another government shutdown. Disagreement over funding — Trump wants $5.7 billion in border wall money — led to a 35-day shutdown that ended Jan. 25, 2019.

To help journalists understand this issue and put it into context, we’ve pulled together academic studies, federal government reports and other scholarly literature. Below, we have summarized research that explains what border barriers are, why they have become so popular and whether they actually help countries control their borders. We have also included research that investigates the consequences of building these barriers, including impacts on the environment and local communities.

It’s important to note that government officials, politicians, scholars and others tend to use the terms “fence,” “wall” and “barrier” interchangeably when discussing man-man structures built to control a country’s borders. There also is some confusion over terms such as “border security.” New York Times reporter Glenn Thrush wrote an article offering a “glossary of the border debate.”




Understanding border barriers


“Why Do States Build Walls? Political Economy, Security, and Border Stability”
Carter, David B.; Poast, Paul. Journal of Conflict Resolution, 2017.

This study looks at the reasons why governments in various parts of the world erected border walls between 1800 and 2014. They refer to border wall construction as a “particularly aggressive strategy” for addressing unauthorized crossings and explain that walls are “almost always evidence that neighbors are not effectively cooperating in managing the border and have inconsistent border management strategies.”

The researchers examined 62 border walls, some of which stretch thousands of miles. France, Israel, Saudi Arabia and the Soviet Union are “the most active users” of border walls, the authors note. In addition, more than half of border walls erected during the last two centuries were built in the post-Cold War era.

The researchers find that territorial disputes are not a consistent factor driving governments to erect walls. Neither is the presence of civil war in a neighboring state. Economic inequality, however, is. “Borders that separate economies with very different levels of development are likely to be unstable,” the authors write. “This instability is associated with a significantly higher probability of wall construction.”

According to the authors, the fact that economic inequality is “the most robust predictor of border walls” indicates that walls built in recent decades were designed to fortify countries against unwanted immigrants and illegal trade.


“Progress and Challenges with the Use of Technology, Tactical Infrastructure, and Personnel to Secure the Southwest Border”
Report of the U.S. Government Accountability Office, GAO-18-397T, March 2018.

This report examines some of the challenges the U.S. Customs and Border Protection (CBP) faces in using technology, border fencing and other resources to control the U.S.-Mexico border. The report, released by the U.S. Government Accountability Office, also criticizes the U.S. Customs and Border Protection and the Border Patrol for not doing more to assess the effectiveness of their efforts.

For example, the report notes that U.S. Customs and Border Protection “has not developed metrics that systematically use data it collects to assess the contributions of border fencing to its mission, as the Government Accountability Office has recommended.” Also, the Border Patrol “has not yet used available data to determine the contribution of surveillance technologies to border security efforts.”

The report spotlights problems in maintaining the border fence. “From fiscal years 2010 through 2015, CBP recorded a total of 9,287 breaches in pedestrian fencing, and repair costs averaged $784 per breach,” according to the report. Parts of the fence have become so degraded they needed replacing. From 2011 to 2016, CBP spent $4.84 million per mile, on average, to replace 14.1 miles of border fencing.


“Barriers Along the U.S. Borders: Key Authorities and Requirements”
Garcia, Michael John. Report of the Congressional Research Center, March 2017.

This 44-page report, issued by Congress’ public policy research arm, offers a close examination of the federal laws and policies that govern how physical barriers can or should be used along America’s international borders. The report also outlines the various laws that DHS can waive for the construction of border fencing – the Safe Drinking Water Act, Archeological Resources Protection Act and the Migratory Bird Treaty Act, for example. In the report, Michael John Garcia, the acting section research manager for the Congressional Research Center, also makes it clear that there are no legal barriers to prevent the expansion of a America’s border barrier.

Garcia explains that after several hundred miles of barrier were constructed between 2005 and 2011, DHS “largely stopped deploying additional fencing, as the agency altered its enforcement strategy in a manner that places less priority upon barrier construction.” Before Trump became president in 2017, federal law already required DHS to build almost 50 miles of additional barrier. However, no deadline had been set for the completion of that expansion, according to the report.


Effectiveness, economic impacts


“Border Walls”
Allen, Treb; Dobbin, Cauê de Castro; Morten, Melanie. National Bureau of Economic Research Working Paper No. 25267, November 2018.

Scholars from Dartmouth College and Stanford University examine how expanding the U.S.-Mexico border fence has affected migration and the U.S. economy. They focus on the segment erected between 2007 and 2010 under the Secure Fence Act of 2006, which added 548 miles of reinforced fencing in Arizona, California, New Mexico, and Texas.

The key takeaway: The $2.3 billion project curbed migration and benefited low-skill U.S. workers but hurt high-skill U.S. workers. “In total, we estimate the Secure Fence Act reduced the aggregate Mexican population living in the United States by 0.64 percent, equivalent to a reduction of 82,647 people,” the authors write.

Researchers find that for each migrant lost, America’s gross domestic product fell by about $30,000. “Because the wall expansion resulted in fewer Mexican workers residing in the United States, economic activity was redistributed toward Mexico, increasing real GDP in Mexico by $1.2 billion and causing real GDP in the United States to fall by $2.5 billion,” they write.

The expansion led to a slight increase in per capita income – an extra 36 cents — for low-skill workers in the U.S. Meanwhile, high-skill workers saw a small drop – an estimated loss of $4.35.

According to the analysis, another fence expansion “would have larger impacts on migration from Mexico to the United States, they would also result in greater reallocation of economic activity to Mexico; for example, a wall expansion that builds along half the remaining uncovered border would result in 144,256 fewer Mexican workers residing in the United States, causing the United States real GDP to decline by $4.3 billion, or approximately $29,800 in lost economic output for each migrant prevented.”

It’s important to note that the researchers’ estimates are based on the number of Mexican citizens living in the U.S. who applied for an identification card from a Mexican consulate in the U.S. It is unclear what percentage of Mexican citizens residing in the U.S. seek a consulate ID card, about 850,000 of which are issued per year, according to the study.

The researchers suggest that instead of expanding the border fence, a better option for reducing migration would be to cut the costs of trade between the two countries. That should result in higher wages in Mexico, the authors explain. Cutting trade costs by 25 percent, for example, “would have resulted in both greater declines in Mexico to United States migration and substantial welfare gains for all workers.”


Population impacts


“Due Diligence and Demographic Disparities: Effects of the Planning of U.S.-Mexico Border Fence on Marginalized Populations”
Wilson, J. Gaines; et al. Southwestern Geographer, 2010.

This study, from researchers at several Texas universities, examines the “social justice impacts” of a DHS plan to erect border fence in certain parts of Texas. Researchers looked specifically at the plan outlined in the DHS’ November 2007 Environmental Impact Statement for the Rio Grande Valley Sector. They focused on the path of the fence through Cameron County, Texas, comparing locations where the USDHS planned to erect fence and locations where they planned to leave gaps. They considered how the project would affect individuals’ use and ownership of the land.

The authors find that the plan, which was later amended, would have had a disproportionate impact on people with lower incomes and education levels as well as Hispanics and people who were not U.S. citizens. The researchers note that it does not appear the federal government studied how the fence would affect communities before devising its plan. The DHS “did not show sufficient due diligence in understanding and mitigating any disparate impacts,” the authors write, adding that DHS “acknowledged that the general placement of the fence along the Mexican border ensures that poor Hispanic immigrant families are those most likely to be affected by its construction.”

The researchers write that although the fence route eventually changed, but they are not clear how it changed. The DHS “has not provided any information indicating that the route changed substantially or that the government considered the characteristics of those who were impacted in making changes to the location of the fence,” they explain.


Environmental impacts


“Border Fences and their Impacts on Large Carnivores, Large Herbivores and Biodiversity: An International Wildlife Law Perspective”
Trouwborst, Arie; Fleurke, Floor; Dubrulle, Jennifer. Review of European Comparative & International Environmental Law, 2016.

This article, which appears in an international law journal, examines border fences’ impact on wildlife and natural habitats from an international law and policy perspective. The authors explain that the characteristics of each type of barrier affects wildlife differently. Existing barriers are made of a range of materials, including concrete, sand, barbed or razor wire and electrified fencing. In some cases, metal walls extend underground. Some fencing strategies involve land mines.

Barriers are of particular concern in Central Asia, home to a variety of migratory and nomadic mammals, the authors write. “By splitting populations, impeding migrations and killing animals attempting to cross, border fences pose an actual or potential threat to many of these, including the Mongolian gazelle (Procapra gutturosa), saiga antelope (Saiga tatarica), Asiatic wild ass (Equus hemionus, also known as khulan), Bactrian camel (Camelus ferus), argali sheep (Ovis ammon) and snow leopard (Panthera uncia),” they write.

The scholars point out that current laws and policies could be improved to prevent and ameliorate the impacts of border barriers worldwide. Barriers “have the potential to undo decades of conservation and international collaboration efforts, and their proliferation entails a need to realign our conservation paradigms with the political reality on the ground,” they write.


“Nature Divided, Scientists United: US–Mexico Border Wall Threatens Biodiversity and Binational Conservation”
Peters, Robert; et al. BioScience, October 2018.

This call to action, which criticizes the U.S.-Mexico border barrier and Trump’s proposed expansion of it, was signed by more than 2,500 scientists representing dozens of countries, including 1,472 from the U.S. and 616 from Mexico. It stresses the barrier’s “negative impacts on wildlife, habitat, and binational collaboration in conservation and scientific research” and offers recommendations for limiting harm.

The authors explain that a continuous border wall or fence “could disconnect more than 34 percent of U.S. nonflying native terrestrial and freshwater animal species … from the 50 percent or more of their range that lies south of the border.” They complain that the border barrier and security operations have obstructed scientific research. “U.S. and Mexican scientists have shared distressing stories of being intimidated, harassed, and delayed by border security officers,” they write.

The scientists offer four recommendations for moving forward, the first of which is for Congress to make sure DHS follows federal environmental laws. “Any future appropriations for border barrier construction and operations should require adherence to all environmental laws and preclude their waiver,” the authors write. “In areas where the DHS has already issued waivers, we call on the DHS to carry out analysis, mitigation, and opportunities for public participation as prescribed by all relevant environmental laws.”

The remaining three recommendations focus on performing surveys to identify species and habitats at risk, avoiding barriers in areas with “high ecological sensitivity” and facilitating “scientific research in the borderlands to complement and assist environmental evaluation and mitigation efforts.”


“Border Security Fencing and Wildlife: The End of the Transboundary Paradigm in Eurasia?”
Linnell, John D.C.; et al. PLOS Biology, June 2016.

In this peer-reviewed article, scientists from Europe and Asia offer their views on how wildlife are harmed by border fencing in Europe, the Caucasus and Central Asia. They specifically discuss the impact on bears, lynx and wolves in Slovenia and Croatia and on khulan and other large herbivores in the southeast Gobi.

The authors point out that they had difficulty finding information on border fences in these regions, especially details on exact location, length and construction of the fencing. “Unfortunately, a systematic overview of these details is lacking, making it impossible to conduct any form of spatially explicit analysis of the real fragmentation effect of these structures,” they write. “There are likely to be very different effects of structures on different species, migratory large herbivores and large carnivores being most affected.”

Another main takeaway: The researchers estimated there is a total of 30,000 kilometers of border fencing in the study area and that Central Asia is one of the most heavily fenced regions on the planet.

The authors stress the need for scientists and policymakers to work together. “The opportunities for transboundary cooperation in wildlife conservation are shrinking in many regions,” they write. “When examining the geopolitical situation and the very real security challenges that some countries in Eurasia are facing at the moment, it seems likely that many of these fences are here to stay and that more are likely to appear, while existing fences are strengthened. This means that conservationists will have to recognise the potential impacts of these fences and adapt population management accordingly.”


Other resources for journalists:

  • U.S. Customs and Border Protection provides background information on its border security efforts, including the historical evolution of its strategies.
  • Some of the scholars with expertise in border barriers include: Reece Jones, an associate professor of geography at the University of Hawaii at Manoa; Elisabeth Vallet, director of the Center for Geopolitical Studies at the University of Quebec-Montreal; Jeremy Slack, an assistant professor of geography at the University of Texas, El Paso who runs the Immigration and Border Communities-Research Experience for Undergraduates; Kenneth Madsen, an associate professor of geography at Ohio State University; and Peter Andreas, a professor of international studies and political science at Brown University.
  • Staff members of the Arizona Republic and USA Today Network won the 2018 Pulitzer Prize in explanatory reporting for their coverage of Trump’s pledge to construct a wall along the U.S.-Mexico border.


Editor’s note: This post has been updated with a more recent number for border barriers worldwide. 

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