If we look at the course of history, at the past of certain events, we have probably thought: "never again". "Never again" such a level of destruction after the atomic bombs on Hiroshima and Nagasaki, "never again" let ourselves be divided by separations, especially ideological ones, like those that gave birth to the Berlin Wall.
Why, then, has the policy of building walls continued to grow steadily over the last thirty years? Will this security complex be able to withstand the future challenges of the international system?
1. Unfulfilled hopes
Walter Benjamin, in his manuscript On the Concept of History, notes: 'The astonishment that the things we experience are still possible in the twentieth century is not philosophical. It does not lie at the beginning of any knowledge except this: that the idea of history from which it derives is not sustainable'.
The fall of the Berlin Wall and the end of the Cold War deeply marked the popular imagination: the end of a world divided into two spheres of influence, separated by conflicts and border disputes had finally been realised. The fall of the wall and the emergence of a new international system that would lead us towards globalisation seemed to doom the concepts of 'state' and 'borders' irrevocably.
The present, however, seems to suggest that these hopes and expectations have been dashed. From 1989 to 2010, in fact, forty-eight new walls were built in the world.
Erecting a wall for defence purposes is probably the oldest instrument and symbol of security invented by man: the walls of Troy, Babylon, the Great Wall of China or Hadrian's Wall.
Barriers created to define the borders of a state, mark the political and cultural differences between different ethnic groups, defend against the enemy's desire to conquer. Moreover, the wall has had and continues to have a precise characteristic: while on the one hand it has the function of dividing from an 'enemy', on the other hand it serves to unite the population that wants to defend itself, creating an identity. By marking a boundary with those who are recognised as 'different' and therefore fearsome, one can also try to eliminate the natural internal divisions of a people.
Unlike in the past, however, in the present each state controls its own territory, which has precise borders, regulated by international law, which the other countries in the world have recognised and decided to respect. The majority of the world's states are members of the United Nations and have signed its Charter, which recognises the territorial sovereignty of each of its members.
What then is the task of a wall in the present time?
In the last thirty years, in the era of globalisation, the purpose of building a wall has become precisely that of blocking, or at least reducing the movement of unauthorised civilians and unregulated goods and services. In the second half of the twentieth century, the global population has grown rapidly from 3 billion in 1960 to around 7 billion today. At the same time, substantial economic differences have emerged between the richest and poorest countries on earth, prompting people to move from rural areas to cities, or even across state borders in search of better job opportunities.
Moreover, in the last thirty years, the number of wars in specific areas of the world has increased, and so have the millions of people forced to flee their countries in search of safety. After 9/11, the relentless search for total security due to international terrorism has found one of its strongest and most immediate symbols in the wall.
In order to describe the contrast and contradiction between the closure of territories, i.e. the impossibility for people in more fragile and precarious living conditions to move around, and on the other hand, a liberal opening up of the economy, meaning the free circulation of goods and services, the two scholars Florine Ballif and Stéphane Rosière invented the expression teichopolitique, "theicopolitics", from the Greek teichos, which indicates precisely the city walls.
2. Theicopolitics: the new characteristics of walls
According to the two authors, theicopolitics is the set of all those policies that materially dissect space on the basis of a principle of securing, protecting and controlling the territory. It then implies the creation of further protection systems, which secure the wall itself and the space in which it is located. The attitude of governments towards the perception of risk, especially after 9/11, has changed to avoid the occurrence of that risk, and thus to increase the control of the security systems themselves, which in themselves perform that very function. The control of the walls, where they have already been built, must therefore also be reinforced.
The walls built in the last thirty years have mainly been built in territories that are still characterised by the presence of: conflicts, as in the case of the wall between Palestine and Israel - or defensive walls built by the US army in some Iraqi cities during the 2003 war - and strong economic disparities, as in the case of the wall between Mexico and the United States, or the one between India and Bangladesh. Normally, the term 'wall' is always or in most cases used. However, depending on the degree of security of the territory in which it is located, it may take on different characteristics and therefore be referred to by different names: there are four types of closed borders, and each of them meets very specific security requirements.
The first type is the border between two states that do not want to connect their territories. This creates a buffer zone in which movement is prohibited and the borders between the two countries are effectively closed, but no artificial barriers have been built. An example of this type is the border between Colombia and Panama.
The second type is instead, clearly visible on the ground. It is a closure that takes concrete form through barriers made of different materials, such as barbed wire, sometimes electric. This type of barrier, for example the one between China and Kazakhstan, has a relatively modest construction cost and those who want to try to cross it have a good chance of succeeding.
The third type of closed border is the actual wall, the concrete wall, which is built in territories at high risk of instability due to conflict or terrorism, or in territories with a high rate of immigration between one country and another: such as the wall between Mexico and the United States or, in the first case, the wall between Palestine and Israel. These walls are characterised by a strong political will to secure the territory and are therefore equipped with additional installations that serve to protect them and to extend and strengthen their range of action even further: alarm systems with activation sensors (on the ground or on the wall), anti-tank defences, video cameras for night-time filming, ground sensors capable of detecting movements over a predetermined distance, lookout towers. Crossing from one side of the wall to the other is not impossible in theory, but practice is far from theory. People and goods wishing to attempt the feat are subjected to extremely strict security and anti-terrorism checks that take days, if not weeks in some cases. Moreover, passage is only possible at certain times or on certain days, which may vary according to government decisions.
The last type of closed border is the front and is characterised by the non-recognition of the border between the two states, which is therefore called 'frozen'. Here the armed forces are omnipresent and crossings from one side to the other are practically non-existent. Kashmir is a case in point.
3. Cost vs. effectiveness
The development of increasingly sophisticated technological systems has made the construction of walls more and more expensive. Let us take the case of the project on the continuation of the wall between the United States and Mexico and try to evaluate it in terms of costs and benefits. The Massachusetts Institute of Technology has produced a rough estimate (assessing the cost of materials, labour and necessary costs) according to which 1600 kilometres of wall (thus a small part compared to the entire border separating the two states) in reinforced concrete, 9 metres high, would cost between 27 and 40 billion dollars. Other estimates put the cost at between 25 and 21 billion dollars (the latter is the estimate made by the US Department of Homeland Security). It is important to stress that these estimates do not take into account the maintenance costs of such a technologically integrated security system as a wall.
The market and the economic interests that revolve around the design and construction of the walls represent a real pressure lobby against governments to convince them to implement the different projects. Let us take the example of the Secure Board Initiative plan between Mexico and the United States, in what began as its first phase in 2006. The contract for the construction of the wall between Arizona and Mexico was won by a consortium of American companies which included Boeing Integrated Defence System, the third most important industry in the export of armaments in the country, after Lockheed Martin and Northrop Grumman.
The US Department of Homeland Security cancelled this project in 2011, precisely because of the high costs involved ($50 million), but it is interesting to note the expected turnover. Among the suppliers of technology to make the wall even more secure was Kollsman Inc., a surveillance technology company based in Merrimack, New Hampshire. Kollsman Inc. is the US subsidiary of Elbit System, Israel's largest privately owned surveillance technology and defence electronics company, which is responsible for the surveillance systems used along the entire length of the wall between Israel and Palestine and which supplies the US military with most of the technology used in the Middle East conflicts.
An effective effectiveness of the complex security system that the walls represent could justify the high costs of their construction and maintenance. According to Reece Jones, professor of geography at the University of Hawaii and author of several books on the politics of wall construction, the effectiveness of these constructions depends on the purpose for which they were built.
In conflict situations, for example, walls do not block contemporary defence systems: drones, planes and missiles can get over the wall just as easily as tanks. In these contexts, the wall is also of no use as a physical border demarcator: the GPS system works much better in this respect and at a much lower cost.
If the purpose for which a wall is built is to stop or reduce illegal trafficking of drugs or weapons, it does not seem to be fulfilling this task well, as in the case of the border between Mexico and the United States. Moreover, it would be difficult to imagine a different situation: the United States is the world's largest consumer of drugs produced in Mexico and, reciprocally, the flow of arms sales from the United States to Mexico is only increasing: more than 2.5 million firearms have crossed the border in the last ten years. This is the reason why the wall has been built.
Do walls then work in contexts of significant migration flows? Yes, these barriers can be effective in these terms, as they are a strong disincentive for migrants to leave, because they represent a real obstacle. In fact, it has been shown that in 1990, in the weeks following the construction of the first section of the wall between the United States and Mexico, between San Diego and El Paso, the percentage of people trying to cross the border dropped to zero. Similarly, the barbed-wire fence built by Bulgaria in 2015 to block migrants trying to reach Europe, reduced the flow substantially.
However, in both cases, after a short time, migrants found another route to get around. When one migration route is closed, another one opens. The wall may block part of the border, but it is not the solution that solves the causes of migration or terrorism. It is a powerful evocative symbol of action: it gives the impression that governments are solving the perceived problem, or made to be perceived as such, in the short term. Perhaps that of the next election.
4. Future challenges
After the fall of the Berlin Wall, defence systems designed around the presence of walls were mainly used to defend the internal security and economy of the countries that built them. Since 1989, however, the international system has become much more complex, beset by severe economic and security crises in which the use of multilateral resolution systems, such as the United Nations, has often been an unexplored or unsuccessful route.
The wall has a dual function: on the one hand it forms the identity of a country, while simultaneously excluding those who would endanger that unity. The International Organization for Migration (IOM) estimates that 70 per cent of the populations surviving in the slums of Dhaka have moved here as a result of environmental disasters such as floods or hurricanes. The wall has a dual function.
"Climate migrants" or "environmental migrants" as they are called, are already a reality in different parts of the world and tens of millions more will be added, because even minor variations in climate can have catastrophic outcomes for local populations. If we apply this scenario to a country like Bangladesh, where health care is poor and education levels are low, it is clear that if one-fifth of a territory floods and part of what remains is not cultivable, millions of people will be forced to migrate. The poorest will be forced to go to India where the world's longest border barrier awaits them: 4050 km. In the face of such massive and desperate movements of people, can one continue to believe that the policy of containment and security of walls is effective?
David Kornbluth, a former Israeli diplomat, always thought that the wall between Israel and Palestine was "a great success. [...] In wartime, Israel is an extremely cohesive country. When war comes, it miraculously regains its unity. Many say that the real threat to Israel is internal divisions, a fragmentation that could bring it to its knees. But it remains a very strong country."
Walls then, perhaps, only serve to conceal any internal divisions and fractures within each country's society, for which governments prefer to shift attention outwards, beyond the wall.
 Didier Fassin, Le vite ineguali, (Milan: Giangiacomo Feltrinelli edition, June 2019)  E. Vallet e C. P. David, “Introduction: The (Re) Building of the Wall in International Relations”, in Journal of Borderlands Studies, Vol. 27, n. 2, September 2012, pp. 111-119.
 Reece Jones, “Borders and walls: do barriers deter unauthorized migration?”, in Migration Information Source, 5 October 2016.  Tim Marshall, I muri che dividono il mondo, (Milano: Garzanti editore, September 2018)  Ibidem  Reece Jones, “Borders and walls: do barriers deter unauthorized migration?”, cit., p. 4.  Christophe Ventura, “Mexique: quel bilan après un an de gouvernement d’Andrés Manuel López Obrador?”, intervista su IRIS-France, 23 January 2020.  Ibidem, p. 6
 Tim Marshall, I muri che dividono il mondo, cit., p. 140.  For more, see the analysis “DALL’ISOLA DI JEAN CHARLES FINO AL GANGE - Non è Jules Verne, queste sono le migrazioni ambientali”, by Rebecca Reina for the Centro Studi AMIStaDeS, 21 May 2020.  Tim Marshall, I muri che dividono il mondo, cit., p. 127.  Tim Marshall, I muri che dividono il mondo, cit., p. 93.
T. Marshall, I muri che dividono il mondo, (Milano: Garzanti editore, September 2018)
D. Fassin, Le vite ineguali, (Milano: Giangiacomo Feltrinelli editore, June 2019)
D. B. Carter e P. Poast, “Why do States build walls? Political Economy, Security, and Boarder Stability, in Journal of Conflict Resolution, Vol. 61, n. 2, 2017, pp. 239-270.
Reece Jones, “Borders and walls: do barriers deter unauthorized migration?”, in Migration Information Source, 5 October 2016.
E. Vallet e C. P. David, “Introduction: The (Re) Building of the Wall in International Relations”, in Journal of Borderlands Studies, Vol. 27, n. 2, September 2012, pp. 111-119.
F. Ballif e S. Rosière, “Le défi des teichopolitiques. Analyser la fermeture contemporaine des territoires”, in L’ Espace géographique, Vol. 38, n. 3, 2009, pp. 193-206.