After the year 2020 ground wars will be more intense and concentrated in the world’s crowded coastal cities. That’s the consensus from a panel of experts including current and retired Army officers and professional analysts.

Over the past decade, the U.S. Army and Marine Corps have adapted to the low-intensity wars in Iraq and Afghanistan by abandoning traditional heavy weaponry for lighter, more mobile systems — and by adding billions of dollars in aerial-surveillance equipment. While perhaps suited to occupation duty, this gear might not last long against a determined, high-tech foe on a coastal, urban battlefield.

The experts differ on how U.S. ground forces should change. But they all agree that big changes are necessary if American forces expect to win the next ground war. Five experts weigh in:

Mark Gunzinger, Senior Fellow, Center for Strategic and Budgetary Assessments
In the aftermath of a decade of operations in Iraq and Afghanistan, America’s Army and Marine Corps are struggling to define how they should prepare to meet future challenges to our nation’s vital interests. In the midst of the debate over how to reconcile the defense strategy with a shrinking budget, both services should consider several factors that are likely to shape the future operating environment.

First, so-called “anti-access and area-denial” threats are not limited to the air, maritime, space and cyberspace domains. The proliferation of guided rockets, artillery, missiles and mortars (G-RAMM) will lead to new challenges for future ground units deployed abroad. The devastating effects caused by Improvised Explosive Devices and Rocket-Propelled Grenades in Afghanistan and Iraq – including the loss of 30 sailors, soldiers and airmen on a CH-47 Chinook helicopter in Afghanistan in August – were crude harbingers of what may occur should terrorist groups and other non-state actors obtain more advanced anti-personnel, anti-air and anti-ship guided weapons. Second, the proliferation of nuclear weapons to North Korea, Iran and possibly Syria and other states could create environments where ground forces would be at significant risk if they are not adequately prepared.

To address these challenges, the Army and Marine Corps must assume that they will not have the same freedom of maneuver that they experienced during operations since the end of the Cold War. New investments are needed to develop effective defenses against G-RAMM and to ensure ground forces will be able to operate in areas where Weapons of Mass Destruction have been used. At a higher level, the Marine Corps should be prepared to act as a crisis-response force and conduct low-signature amphibious operations to help open the way for follow-on joint-force deployments, while the Army could focus on Foreign Internal Defense missions in peacetime and capabilities needed to conduct a large counter-WMD operation.

These shifts do not mean the land services should divest their hard-won Irregular Warfare competencies. On the contrary, the Army and Marine Corps should preserve their ability to support IW operations, albeit on a much reduced scale, as they develop new capabilities needed to fight tomorrow’s wars.

Col. Gian Gentile, Professor of History, U.S. Military Academy
We should absolutely avoid building a future ground force optimized for wars like Iraq and Afghanistan. Whatever future conflicts U.S. ground forces may face, we can be sure they will be quite lethal, ranging from state-on-state warfare to hybrid warfare and low-end guerrilla wars.

The likelihood of another Iraq or Afghanistan in the next 10 years seems doubtful; instead one can imagine ground operations that will be much more limited in time and in scope. Light infantry constabulary forces optimized for wars like Iraq and Afghanistan will be highly vulnerable and open to catastrophic destruction in this lethal, future environment. Future land battlefields demand a ground force built around the pillars of firepower, protection and mobility.

Moreover, this future ground force needs to be able to move and fight in dispersed, distributed operations in an age where widespread access to Weapons of Mass Destruction means a ground force that concentrates can be easily annihilated. Much will have to change in order to transform the Army and Marines to ground formations of this type, but that transformation is critical.

Lt. Gen. (ret.) Dave Barno, Senior Fellow, Center for a New American Security
The typical land battlefield of 2021 will be a complex, often urbanized environment where battles are often fought inside the dense urban sprawl that increasingly proliferates along the edges of the world’s great cities. Generals will be loath to conduct large-scale operations in these very difficult environments, but the reality is that more and more of the world is trending in this direction. The ability to operate effectively in this space will be a sine qua non of most future military operations on land.

Littoral spaces guarding the free flow of vital natural resources deserve particular attention in the world of 2021. U.S. and allies’ dependence on the unrestricted flow of global energy supplies makes the chokepoints through which that energy transits the new “strategic high ground.” Army and Marine capabilities to project power into the littoral spaces which control nearby constricted waters (e.g., the Straits of Hormuz) will be increasingly important.

In the world of 2021, the prime threats arrayed against U.S. ground forces are less likely to be roadside bombs and suicide attackers than ever-improving conventional weaponry such as man-portable anti-tank missiles and small arms. These weapons remain abundant in many of the most likely contested areas around the world.

In this volatile, shifting mix of conventional and unconventional tactics and weaponry — often called “hybrid wars” — designing the right systems to equip U.S. ground forces is a monumental challenge. A balance must be struck between protection — demands for which rapidly escalate in a static hostile environment — and mobility. The right trade-off for an uncertain future may be highly mobile vehicles which offer substantial infantry protection from conventional weaponry, but not from massive roadside bombs.

In a future of complex urbanized combat, moving protected infantry around the battlefield and building the individual soldier into a highly capable fighting platform is the new material priority for ground-force development. Enabling small units to reliably leverage networked technology for access to fires, to employ unmanned and robotic adjuncts and operate mobile fighting systems will be a key sector for investment.

Ultimately, future ground war will be about small-unit leadership and the ability to conduct highly decentralized, often autonomous operations. It will require leveraging a networked command-and-control capability to rapidly access precision fires or to concentrate with other small units. Priority should be given to the ability to fight and communicate in an urbanized environment, with the highly enabled infantry squad as the new primary fighting unit.

Dave Kilcullen, former adviser to Gen. David Petraeus, currently CEO, Caerus Associates
We’re going to have get better at fighting unplugged — fighting without necessarily having access to GPS and GPS-enabled and satellite-based stuff, primarily because the enemy can use that stuff, too. You could be in an environment where they turn it off for you, or you have to turn it off. The ability to fight with electronic superiority that we have now is going to go away.

The guys in the ground forces need to get heads around the idea that we’re not going to maintain air superiority in the future. We’ve become trusting in the idea that we’re always going to have a friendly sky above us, with U.S. forces dominating the sky. The way things are going, it’s not beyond the realm of possibility that we’ll find ourselves in a conflict where we don’t have air superiority or where the enemy can create its own temporary air superiority. That changes the ground environment dramatically.

When you’re engaging in an urban environment you need to break your force down into smaller bits so it can fight isolated. The Army talked about modularity 10 years ago. But the Army stopped modularity at the brigade level. We need to take that down to a much lower level. The Marines call that distributed operations. The Army and Marines need to take a second look at how to do modern, distributed operations in an urban, coastal environment. It has implications for weapon systems and communications. It’s very hard to communicate in an urban environment. Things like imagery … as soon as you go into an urban environment, you can’t see things on the ground around you. Just mapping where you are becomes very difficult.

One of the things really bothering me is the spread of drone technology. We have dominated the drone field, with the exception of Israel, for last the decade. We never really had to deal with environments where the enemy has drones as well. Within a decade we’re going to be in that environment. Two weeks ago the Mexican police had a drone crash in El Paso. The Iranians have them. Hezbollah has them. We’re going to be in an environment soon where it’s our drones versus their drones. That will be a big shift for ground forces.

A lot of people draw a false dichotomy between conflicts against China or North Korea and urban conflict in, say, Iraq or Afghanistan. But if you look at what’s involved on the ground in fighting against China, you find it’s very much the same stuff: urban, coastal and networked. I’m not suggesting any of these conflicts is likely, but state-on-state conflict doesn’t always mean conventional warfare. It’s still going to be very messy and complex on the ground.

P.W. Singer, Senior Fellow, The Brookings Institution
To many, the U.S. military has rounded an intellectual corner in the last few years. There has been an increased emphasis on the ability to navigate the complex geographic and social patterns of simultaneously defeating a guerrilla army while winning tribal elders’ hearts and minds in the midst of perhaps the most rural, remote, and mountainous part of the world. Yet the rest of the world seems to be going in a different direction than the type of villages we are training for, which remain essentially unchanged from the time of Alexander the Great’s invasion to our own operations in rural Afghanistan. Rather than its rural history, the future of humanity lies in the cities.

More than 40 percent of the world’s population already lives in cities with populations of more than 1 million. These staggering statistical trends are driving the evolution of the “megacity,” an urban agglomeration of more than 10 million people. Sixty years ago, there were only two: New York and Tokyo. Today there are 22 such megacities, the majority in the developing countries of Asia, Africa and Latin America. By 2025, there will be another 30 or more.

Most importantly, each of these cities is characterized less by its glittering skyline than by its “megaslums,” the miles upon miles of shantytowns and squatter communities that house millions of young, urban poor — the angry losers of globalization. What this means is that despite our understandable current focus on how to deal with tribal elders in the mountains of Afghanistan, the numbers tell us that the future focus of global security will most likely be an urban one.

This shift is not just because of the mass movement into the cities, but it is also because the city is increasingly where the anger that causes insurgency, terrorism and war originates. Moreover, these broken cities are their home turf, the more likely Sherwood Forest to any future insurgent or terrorist than a village or forest itself.

The lesson we should take away from these trends is that as important as the concern over the next year in Afghanistan or the looming rise of China is, policymakers must also be mindful that there are even broader changes afoot. For those who care about peace, the same lessons hold. One can either ignore these new domains, the non-strategy of merely hoping for the best, or stave off future conflict and crisis by establishing the norms and institutions needed to stabilize and regulate the new spaces shaping our world.