by Robert Beckhusen. Robert Beckhusen is a freelance writer who contributes regularly at War is Boring. He’s also written for publications including C4ISR Journal, Wired, The Daily Beast and World Politics Review. You can follow him on Twitter.

If you want to picture the characteristically 21st century living environment, imagine cities like Lagos and Shanghai; or Sao Paulo, New York and Cairo. Now double the population, and you have a pretty close approximation of what the world’s largest urban areas will be like by mid-century.

Now ask: How does the Army control a city of that size? How does an infantry force of thousands cut off and surround and city of 10 million? What about 20 or 30 million? The answer is that the United States can’t, at least not yet.

That’s the conclusion of a study released in June from the U.S. Army’s Strategic Studies Group. Researchers from the group’s Megacities Concept Team spent a year visiting the world’s megacities — defined as having a population greater than 10 million people — to study how the Army might conceivably fight a war inside them.

“The Army, and the [Department of Defense] community more broadly, neither understands or prepares for these environments,” the report states. The result is that the Army’s fundamental assumptions about urban warfare will collapse when it’s tasked with intervening in the growing megacities of the future.

Emphasis on when. The Army does not have experience fighting in megacities, but sees conflict in these cities as an inevitability due to their strategic importance. Even the Army’s experience in Baghdad — population 6.5 million — is of a smaller scale compared to the really massive and growing megacities in Asia, Africa and Latin America. As a comparison, the Army notes there will be an estimated “37 cities across the world that are 200-400 percent larger than Baghdad” by the year 2030.

To simplify why the U.S. is having trouble, it’s because the way the Army normally plans for urban war is similar to how it plans for war everywhere else. This is generally by having the approaching — or attacking — element attempt to shape its environment in order to gain tactical, operational and strategic surprise and advantage over its foe. This forces the enemy to react to your moves, rather than the other way around.

A classic example is for the advancing force to maneuver around a city in order to threaten the defending force’s lines of supply — which are simultaneously targeted with stand-off weapons such as artillery and air strikes. The attacking force also targets the defenders and the civilian population with propaganda and psychological warfare. The U.S. military’s 2003 “shock and awe” campaign towards Baghdad is an example of this strategy, the main exception here being the tank-driven “thunder runs” into the heart of the city as the Iraqi army collapsed.

Megacities totally disrupt this strategy for a load of reasons. “The scale of megacities, in essence, defies the military’s ability to apply historical methods,” the report states. To use one example, Lagos, Nigeria contains more than 20 million people packed into 910 square kilometers of rickety urban sprawl. This environment is so huge, it cannot be feasibly surrounded with any force the U.S. could reasonably expect to deploy. Were the U.S. to intervene in a conflict, it couldn’t realistically control the flow of people, goods or communications — everyone has cell phones. There’s no element of surprise. The military could barely even maneuver inside the city, for the simple fact that there’s too much traffic and many of the streets cannot support heavy logistics vehicles.

“The congestion of ground avenues of approach, combined with the massive size of the megacity environments, makes even getting to an objective from the periphery questionable, let alone achieving an operational effect,” the report states.

Another problem for military planners is that each megacity is very different from one another, which undercuts a lot of the military’s assumptions when creating doctrine. To use a comparison, let’s say you’re in charge of leading troops up an enemy-controlled hill. The hill could be in Vietnam, Panama or Afghanistan. In any case, the attack will generally follow a set of similar rules. One hill — while having its own unique characteristics — will be a lot more like another hill than one megacity is to another.

Just compare the differences between Lagos and — to use another example — Sao Paulo. Or the difference between either of those cities and Bangkok and New York. Transportation infrastructure, social inequalities, social conflicts, the capabilities of city administrators, the presence of ad-hoc militias — all of these factors vary so much that you require an entirely unique doctrine for operating in each city.

Another problem is that megacities can make conflict more likely. This is less likely in a relatively smoothly-operated place like New York, but the same social pressures that exist there — gentrification, rising inequality and over-crowdedness — are on overdrive in a seething metropolis like Sao Paulo, with its millionaire elites riding to work in helicopters above AK-47-toting drug traffickers who control the streets.

The Army’s Strategic Studies Group doesn’t make many specific recommendations about what to do — except for the Pentagon to start thinking seriously about it. It simply poses questions, such as showing a photo of the crowded skyline of Dhaka, Bangladesh with the words, “How many soldiers does this require?” It also asks how Special Operations Forces and how the military’s own institutions can start figuring out the nuts and bolts of controlling the unimaginably huge cities of the future.