Small Wars Journal

On the Likelihood of Large Urban Conflict in the 21st Century

Sat, 03/25/2017 - 11:56am

On the Likelihood of Large Urban Conflict in the 21st Century

Sean M. Castilla

Zeravani soldiers conduct urban combat training near Erbil, Iraq, February 2017.[i]

The Chief of Staff of the Army, General Milley, recently said “future war will be largely fought in urban terrain,” and that the Army is currently “suboptimized for urban capabilities.”[ii] In recent years several articles have explored how to go about ‘optimizing’ for future combat scenarios in megacities – urban centers with populations of 10 million persons or more. [iii]  Despite this growing emphasis on megacity contingencies, many question the premise of U.S. participation in megacity conflict. 

As Major John Spencer (Modern War Institute at West Point) recently noted, the counterargument is that megacity terrain is too challenging in terms of scale and complexity, and consequently it should be considered an “impossible mission and, therefore, not one we will undertake.”[iv]  Like Major Spencer, I reject this notion. 

This logic is flawed for four reasons.  First, humans, and by extension sources of human conflict, are concentrating in urban areas.  Second, our potential adversaries will continue to leverage complex terrain, such as large urban areas, to negate U.S. advantages. 

Third, dismissing megacity conflict as extreme ignores the fact that conflict in large and complex urban terrain is a prominent feature of 21st century warfare.  Lastly, as the sources of conflict grow increasingly consolidated in urban terrain it is the duty of military professionals to consider the character of such conflict and what types of military options we can provide our political leadership in a crisis.  In this essay I will consider each of the four factors outlined above in further detail.

Global Urbanization Trends

By now, even the most casual reader on this topic knows that global urbanization trends are making conflict in megacity environments increasingly likely.  Urbanization of the global population over the last five decades has been momentous; two centuries ago only three percent of humanity lived in cities, whereas today for the first time in history half of the world population lives in urban areas.[v]  If current urbanization trends continue, over 70 percent of the global population will reside in cities by the year 2050.[vi]  Much of this urban growth will be absorbed in Sub-Saharan Africa and Asia, geopolitical areas that are challenged by rampant poverty and violence.[vii]

The rising socioeconomic influence of megacities (14 percent of global economic output today comes from the world’s megacities), compounded by multiple drivers of instability (i.e. unregulated growth, urban slums, ungoverned areas, income disparity, substandard infrastructure, corrupt governance, sectarianism, climate change, etc.), has significantly bolstered their strategic importance.[viii]  Cities are increasingly rivaling nation states in importance as the driving force in shaping global stability and development.[ix]  As General Milley recently noted, war is about politics and it will be fought where people live; in an urbanized world, large urban areas are the battlefields of the future.[x]

Unforeseen Drivers of Urban Conflict

Another potentially unforeseen, and less obvious, driver of conflict in megacities may prove to be the current modernization efforts of the U.S. and our potential adversaries.  Having observed U.S. military operations in Iraq and Afghanistan, revisionist powers (i.e. states that seek to challenge the status quo of the international system, such as Russia) have adapted their military strategies and modernized their forces to counter U.S. strengths and exploit U.S. weaknesses. 

These adversarial efforts seek to “fracture” the AirLand Battle paradigm by denying U.S. Joint forces supremacy and interoperability across all domains.[xi]  Focused on the current fight, the U.S. simultaneously allowed its modernization efforts to atrophy.  Consequently, revisionist states have achieved technological parity, and in some instances superiority, with the U.S. by implementing robust anti-access/area-denial (A2/AD) networks comprised of a sophisticated array of sensors and cross-domain capabilities (e.g. precision-guided munitions, cyber/electronic warfare capabilities, etc.) designed to challenge U.S. domain supremacy.[xii]

Recognizing these challenges, the U.S. Army is taking action to modernize its force, pacing its efforts on the technological advancements of near-peer competitors.[xiii]  The Army seeks to enhance its air and missile defense, fires, communications, aviation, and cyber/EW capabilities as well as providing lethality and survivability upgrades for the Abrams, Bradley, and Stryker.  Other emerging technologies, such as autonomous drones and artificial intelligence, are being developed to offset the advantages of potential adversaries.[xiv]   

Ultimately, the goal of these modernization efforts, known broadly as the DoD’s Third Offset Strategy, is to shore up the eroded credibility of U.S. conventional deterrence in order to ensure stability in an increasingly competitive multipolar international system.    

If we assume that these modernization efforts prove successful in (a) negating competitor capability advantages in the near-term; and (b) regaining domain superiority in the long run; then it is logical to assume our modernization efforts may inadvertently compel revisionist state adversaries (or their proxies) to challenge U.S. supremacy in the very places we seek to avoid – areas of severely restricted terrain that deny U.S. land forces the ability to maneuver and mass its forces. 

As the world grows increasingly urban, this includes the severely restricted terrain of megacities.  Operating from within such crowded and complex terrain, revisionist states can challenge the international status quo indirectly using deception, misinformation, surprise and speed to engage us below the threshold of military escalation.[xv]  In a 2013 document outlining his view of 21st century warfare, the Russian Chief of the General Staff outlined exactly this kind of indirect approach:

Frontal engagements of large formations of forces at the strategic and operational level are gradually becoming a thing of the past. Long-distance, contactless actions against the enemy are becoming the main means of achieving combat and operational goals.[xvi] 

It may be that as the U.S. reestablishes the credibility of its deterrence capabilities, revisionist forces will choose to launch such non-frontal attacks from the cover and concealment that complex urban terrain provides.

Additionally, while U.S. defense spending continues to vastly exceed that of our competitors, it may be logical for potential adversaries to use complex urban terrain as a base from which to strike the U.S. rather than to continue their modernization efforts for linear force-on-force conflict.[xvii]   Policy advisor and columnist Rosa Brooks recently wrote that U.S. military conventional capability dominance makes it “suicidal” for competitors to directly challenge us.  Revisionist powers are forced to pursue asymmetric strategies (e.g. striking U.S. forces from complex, non-linear battlefields) to counter U.S. strengths and exploit U.S. weakness.  Brooks notes:

We assume that military technological innovation is a one-way ratchet.  High-tech measures taken by one side will be followed by high-tech countermeasures taken by the other, which will be met with still more advanced counter-measures, and so on, ad infinitum…for all our technological sophistication, warfare has never truly moved past sticks and stones – and even today, their bone-breaking power remains surprisingly potent...[sometimes] the most successful countermeasures are low-tech – and historically, this has been demonstrated just as often as has the opposite.[xviii]

Accordingly, it is unnecessary for potential adversaries to match current U.S. modernization efforts tit-for-tat.  Urban terrain offers tactical advantages to the defender that is otherwise inferior at the operational and strategic level.[xix]

A hunter-killer drone with attached net captures a Phantom 3 drone, December 2016.[xx]

By operating within a megacity environment, U.S. maneuver formations will be unable to maneuver with ease and unable to mass its forces at decisive points.  It is not hard to envision scenarios in which U.S. technological advantages can be negated by technologically unsophisticated means in such environments. 

Commercially bought quadcopters configured as low-tech bombers and vehicle-borne improvised explosive devices become just as effective as technologically sophisticated aircraft and tanks in such terrain.  Drone swarms can be disrupted or rerouted by the combination of low-tech obstacles, small arms, obscurants and traps emplaced at urban canyon choke points (imagine our adversaries trawling for drones!).  Robots using artificial intelligence to identify targets will find that, unlike the air and sea domains, the land domain is crowded and complex; they will find themselves drowning in the sea of humanity residing in megacities.  Such scenarios evoke LTG McMaster’s “vampire fallacy” which warns that faith in technology “neglects war’s uncertainty based mainly on interactions with determined and elusive enemies.”[xxi]

Before proceeding, let us then assume that it is plausible that future U.S. adversaries are just as likely to be near-peer, hybrid or asymmetric forces operating in megacities or large urban areas, as they are to be peer competitors conducting force-on-force warfare in open terrain.  Let us also assume that such conflict will be conducted amidst dense human populations that are burdened by poverty, sectarianism, and other social challenges. 

Conflict in Large and Complex Urban Terrain is a Prominent Feature of 21st Century Warfare

Into just its 17th year, warfare in the 21st century has been notably urban in character.  Consider the abundance of urban battles and campaigns that have occurred in just under two decades: Grozny; Nablus; Baghdad; Fallujah; Bint Jbeil; Nahr al-Bared; Tskhinvali; Rio de Janeiro, Gaza; Donetsk; Aleppo; etc.  These conflicts are only the continuation of a trend towards the urbanization of conflict that intensified in the 20th century (reference Stalingrad, Manila, Hue City, etc.).  Recent conflicts such as the Third Battle of Fallujah, operations in Yemen, and the ongoing Mosul campaign suggest that this trend towards urban conflict is not going away.

Despite evidence that war is growing increasingly urban, there are many that continue to dismiss the notion that we should prepare for megacity conflict because it is an unlikely scenario.  Perhaps this reluctance is rooted in our cultural aversion toward conflict in urban areas.  Whatever the cause, the notion that we shouldn’t be preparing for megacity conflict because it is unlikely is akin to saying that we shouldn’t have a React to Nuclear Hazard/Attack battle drill because that scenario is also unlikely.  Training and preparing for the worst case scenario is what we are paid to do.  Choosing not to prepare for such scenarios neglects our duty to be prepared for conflict in whatever form it may arise.  As Roger Spiller noted in Sharp Corners: Urban Operations at Century’s End, “No fighting force is ever permitted to indulge its operational preferences with impunity.  War and lesser forms of conflict do not organize themselves for anyone’s benefit.”[xxii]

Furthermore, as military professionals we must not lose sight of the forest for the trees.  In discussing potential conflict in megacities it is easy to get wrapped around the categorical distinction that they are comprised of 10 million persons or more.  Megacity populations are daunting and it is hard to wrap one’s mind around how to successfully operate in such an environment.  Yet even if conflicts don’t occur in the extreme megacity populations, the overarching argument in this paper is that conflict is likely to become increasingly urban.  Conflict in cities below the megacity threshold will still feature the key characteristics of urban conflict: creating massive casualty rates; requiring considerable resources and time; causing civilian hardship, etc.  The city of Aleppo, with a prewar population of approximately 2.3 million, has been no less ghastly than conflict in a megacity may be.[xxiii]

It is Our Duty as Military Professionals to Consider the Character of Megacity Conflict

Urban conflict will likely continue to be a prominent characteristic of 21st century warfare.  As large cities grow increasingly influential, it is reasonable to assume that we may find ourselves operating in severely restricted urban terrain.  Urban fighting will be extreme.  It will be complex, intense and offer our adversaries many advantages.  It will not be ground of our choosing.  But we must prepare ourselves for such contingencies.  Spiller wrote:

U.S. Army Soldiers use a rooftop as an observation post in Mosul, Iraq, March 2017.[xxiv]

Human behavior has always been equal to the savagery of war, no matter how extreme.  And in the beginning, no other form of early combat posed the test of intense, prolonged, unremitting violence as did combat in and against cities.[xxv]

Going forward I recommend research into the following areas: (1) the character of megacity conflict; (2) the types of operations required in megacity conflict; (3) they types of units required to conduct megacity operations; (4) how to conduct multi-domain Joint combined arms operations in a megacity area of operations. 

End Notes

[i] Carlson, J. (Photographer). (2017, February 14). Germans Train Zeravani Soldiers in Urban Combat (1 of 10) [digital image]. Retrieved from

[ii] Lee, Connie, (2017, March 21). “Milley: Army Will Have to ‘Optimize’ for Future War in Urban Environments,” Inside Defense. Retrieved from  

[iii] Army Capabilities Integration Center, The Megacity: Operational Challenges for Force 2025 and Beyond, 2014,; U.S. Army, ATTP 3-06.11: Combined Arms Operations in Urban Terrain, June 2011, A-1.

[iv] Spencer, John, “What an Army Megacities Unit Would Look Like,” Modern War Institute at West Point, March 8, 2017,

[v] Jonathan Kalan, “Think Again: Megacities,” Foreign Policy 206, May-June, 2014, 69; Halvard Buhaug and Henrik Urdal, “An Urbanization Bomb? Population Growth and Social Disorder in Cities,” Global Environment, 23(1), 2013, 1,

[vi] Kalan, 69.

[vii] Buhaug, H., & Urdal, H. (2013). An Urbanization Bomb? Population Growth and Social Disorder in Cities. Global Environment Change, 23(1), 1-10.

[viii] Kalan, J. (2014). Think Again: Megacities. Foreign Policy, 206, 69-73; Harris, Marc; Dixon, Robert; Melin, Nicholad; Hendrex, Daniel; Russo, Richard; Bailey, Michael, Megacities and the United States Army: Preparing for a Complex and Uncertain Future, June 2014, 21,; Shunk, D. (2014, January 23). Mega Cities, Ungoverned Areas, and the Challenge of Army Urban Combat Operations in 2030-2040. Small Wars Journal, retrieved from

[ix] Robert Muggah, “Fixing Fragile Cities: Solutions for Urban Violence and Poverty,” Foreign Affairs, January 15, 2015,

[x] Lee.

[xi] Perkins, D. G., “Multi-Domain Battle: Joint Combined Arms Concept for the 21st Century,” Association of the United States Army, retrieved from

[xii] West Point Society of Washington and Puget Sound. (2016). General Mark A. Milley, AUSA Eisenhower Luncheon, October 4, 2016 [transcript]. Retrieved from; GEN David G. Perkins, “Multi-Domain Battle: Joint Combined Arms Concept for the 21st Century,” Association of the United States Army, November 14, 2016,; Dr. Albert Palazzo & LTC David P. McLain III, “Multi-Domain Battle: A New Concept for Land Forces,” War on the Rocks, September 15, 2016,

[xiii] Pellerin, Cheryl, “Deputy Secretary: Third Offset Strategy Bolsters America’s Military Deterrence,” U.S. Department of Defense,

[xiv] Judson, Jen, “Army Details Draft Robotics and Autonomous Systems Strategy at AUSA,” Defense News, October 4, 2016,; Martin, David (Correspondent), & Walsh, Mary (Producer). (2017). The Coming Swarm [Television series episode]. In J. Fager (Executive producer), 60 Minutes, New York, NY: CBS Television Network, retrieved from

[xv] Perkins.

[xvi] Galeotti, M. (2014, July 4). The ‘Gerasimov Doctrine’ and Russian Non-Linear War [Web log post]. Retrieved from

[xvii] Abadi, Mark, “The Only Chart You Need to See to Know That the US Spends More on Its Military Than the Next 11 Countries Combined, Business Insider,

[xviii] Brooks, Rosa (2016). How Everything Became War and the Military Became Everything: Tales from the Pentagon. New York, NY: Simon & Schuster, pp. 329-331.

[xix] Spiller, Roger J. Sharp Corners: Urban Operations at Century’s End. Command and General Staff College, Fort Leavenworth, Kansas.  Retrieved from

[xx] Farnsworth, W. (Photographer). (2016, December 13). 2016 AFRL Commanders Challenge [Image 1 of 20] [digital image]. Retrieved from

[xxi] McMaster, H.R., “Discussing the Continuities of War: The Defense Entrepreneurs Forum,” Small Wars Journal,

[xxii] Spiller, vii-viii.

[xxiii] Profile: Aleppo, Syria’s Second City. (2016, November 28). Retrieved from

[xxiv] Manne, A. (Photographer). (2017, March 7). Coalition Forces Conduct Mortar Fire Mission [Image 4 of 5] [digital image]. Retrieved from

[xxv] Spiller, 38.


About the Author(s)

Major Sean M. Castilla is an Armor Officer currently serving in Headquarters, Department of the Army staff as part of the Joint Chiefs of Staff/Office of the Secretary of Defense Internship.  Previous assignments include the 1st Cavalry Division, Special Operations Command Africa, and the 101st Airborne Division.  He holds a M.P.M in Policy Management from Georgetown University, an M.A. in International Relations from St. Mary’s University, San Antonio, and a B.A. Psychology from the University of Texas, Austin.


If any one has doubts take a hard look at Mosul.
Or Aleppo for that matter.
In fact both might be contrasted as the Russian, Assad, Shiite Iranian solution and the other the American way of coalition war.
It isn't simply the combat that is the problem severe oppression by the Islamic State has created millions of migrants and refugees, that have had a significant impact on Europe. In the mean time to get the Islamic State out of Mosul
it has taken months to develop a plan, resolve coalition frictions between member states, and even with what may seem like undue foot dragging collateral has occurred on what is deemed an unacceptable level, if you are the USA.
This is a great paper. I hope it will help us learn lessons from the not quite megacity examples in contrast; Aleppo and Mosul.


Mon, 03/27/2017 - 5:24am

In reply to by mred

Reading the article and the comment I was struck by mred's last sentence on capacity. So mindful of recent events in Northern Ireland, with a focus on Londonderry or Derry, it is useful to go back to events there in July 1972.

The British government authorized a military operation to retake the enclaves in Belfast and Londonderry, that were controlled by he Provisional IRA. This was known as Operation Motorman and involved twenty-seven infantry and two armoured battalions; probably then half the British Army's infantry. All for relatively small urban areas. Armed opposition was expected, but did not happen. See: and for some of the contortions required to get this done, from a probably partial source:…

For those who prefer the audio-visual there is a 2012 documentary, locally made and after The Good Friday Agreement, so has all sides contributing:

I've been fortunate to have had opportunities to sit in on several Megacities working groups, conferences, and table-top exercises. Definitely a topic worth discussion because it involves technological, doctrinal, tactical, and operational problems that will inevitably come to fruition, and it offers opportunities to think, experiment, and innovate solutions. However, one issue seemed to be almost always dismissed early — capacity. Not sure how we solve that one, but I think we need to be very aware and cautious of the urban environment's capacity devouring nature.