Do Good Fences Make Good Neighbors? Border Barriers and the Transnational Flow of Terrorist Violence

Around the world, more and more fences are being constructed along national borders.  Since the end of World War II, sixty-two barriers have been erected between neighboring countries. Forty-eight of those barriers have built since the fall of the “iron curtain.” And most recently, the war in Syria and the resulting outpouring of refugees has even prompted some members of the European Union to begin building fences to close their borders.

The accelerating pace of barrier construction around the world conflicts sharply with our expectations of an increasingly globalized world.  The material benefits of transnational exchange in an increasingly globalized economy have led many observers to anticipate the erosion of state territorial control and ultimately the obsolescence of state borders.  But states appear to be fighting back.

What has inspired so many national leaders to construct physical barriers to defend the territorial integrity of their states despite the economic benefits of globalization?  While their motivations are clearly diverse, one of the most common justifications for the building of walls is the threat of terrorism.  While globalization promises material rewards, it also threatens to bring violence in the form of individuals who may cross state borders unnoticed.  Terrorists can utilize the same infrastructure of communication and transportation technology that promotes trade and capital flows to deliver violence with greater effectiveness to a wider audience.

But fences are an expensive solution to the problem of terrorism, and they may even erode friendly and mutually beneficial relations with neighbors.  Thus the construction of barriers should not be undertaken lightly. Some observers have suggested the reliance on terrorism as a justification of barrier construction is a response to public fears of terrorism rather than an effective tool for keeping citizens safe.  This “security theater” view of border fences could be construed either as a well-meaning but misguided response to public opinion, or as a more sinister attempt at building public support through demagoguery and fear.

Much of this polarizing debate over border barriers has become a clash of increasingly strident opinions rather than an evaluation of facts. Surprisingly, we know very little about the actual effectiveness of border fencing as a counter-terrorism tactic.  We hope to contribute to this debate by providing some evidence about the impact of fencing on the flow of transnational terrorism. 

Our new dataset records information on which states have constructed fences against which of their neighbors since the beginning of the 20th century, as well as information on the dates of construction and dismantlement.  We compare these data on border barriers to data on the annual flow of transnational terrorist attacks from the ITERATE dataset from 1968-2007.  Not surprisingly, a naïve comparison of fenced and unfenced borders reveals that fenced borders experience more terrorism.  In fact, while terrorism is always rare, fenced borders have nearly a 50% higher annual relative risk of experiencing a terrorist attack.

But fences may be a strategic response to prior terrorist attacks – as well as a variety of other factors – and so fenced and unfenced borders will systematically differ in a variety of ways that make a simple comparison unreliable.  We address this problem through statistical matching that compares fenced borders to a set of unfenced borders that are similar in terms of the history of terrorist attacks and a variety of other factors that are known to influence the incidence of terrorism. 

Our results indicate that border barriers can be highly effective tools against terrorism.  Specifically, we find that the presence of a fence reduces the annual probability of a terrorist attack relative to a comparison set of similar borders by 13%.  This reduction represents a 67% drop in the relative from relative risk of a terrorist attack as compared to a similar but unfenced border.

Our results may provide an answer to the apparently puzzling increase in the number of border fences being erected around the world.  These fences are often touted as counter-terrorism tools, and they appear to be effective.  We cannot, of course, assess the extent to which politicians publicize the construction of fences as a response to popular fears.  Moreover, it is important to emphasize that our results only apply to the effectiveness of border barriers in dampening terrorism – as opposed to illicit drugs, illegal immigration, or other criminal activity. However, we do find that border fencing has been an effective tool for states seeking to defend their citizens and their territorial integrity against the threat of terrorism in a globalizing world.

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