How would warfare change if everyone were concentrated into giant cities?

Question

Due to environmental concerns (very cold winters) humans are concentrated into a few large cities all around the world; smaller isolated settlements die out quickly. These cities would form the basis for nations, and each nation would usually be composed of only one city. A typical city would span many dozens of kilometers in radius and be self sufficient at least during the winter. These cities are, of course, built around rivers, lakes, and other high concentrations of important natural resources such as coal and forests for heating, iron for making tools and building and whatever other resources a city would need. Resources found farther out would have to have temporary camps and operate at a high output during the summer to make up for lost time during winter. If two city-states went to war against each other how would these wars play out? Massive multi-year sieges or would the enemy city be ignored altogether in favor of gobbling up the natural resources on their territory? Keep in mind that it is an unspoken rule of sorts that armies don't really fight each other during winter and instead focus on their own survival, I imagine this would make sieges difficult.

The period of technology I am focusing on would be late 19th century so there would be fairly modern artillery, bolt action rifles, early machine guns, etc.

Edit: It is not impossible to keep an army alive in the field during winter granted you have properly prepared and are well supplied, however don't even consider doing any kind of mobile warfare during the winter months.

Answer 1

Cultural Homogeneity, Logistics & Transportation, and The Spring Race:

At first I was skeptical of your planned society, and I think it would still be a bit more dispersed than you think (especially with 19th century tech), but I have family that lived in rural Saskatchewan, and they left their farms every winter to move to town. So while I think there would be more cities than you think, I'll go with it.

There are a number of factors in such a world that could significantly affect war in your world.

• CULTURE: First, with everyone in the country retreating to a central city every winter and living together in cramped quarters, there will be a considerable amount of cultural homogeneity caused by this. People from very disparate parts of the country will share food, language, customs, and intermarry to a much greater degree than in our 19th century world. "Local" people will have a strong national and cultural sense, so capturing populations will be very problematic. Similarly, people in a village just miles away from a foreign nation may have more in common with people on the other side of the empire than those just a few miles away.
• LOGISTICS: For a system like this, with so few cities, there will need to be a very powerful central government with a massive and efficient bureaucracy. This move in population will represent a centralization of all food collection and storage, a stockpiling of vast resources, and an insanely large and efficient transportation network to facilitate the shifting back and forth of not only all the people of the country, but all the livestock and valuables as well. The concentration of population will mean an efficient sanitation system and extremely advanced medical system to deal with all the diseases spread as every sick person in the country is regularly shipped to the same destination with all the healthy people. Policing will need to be very robust as every criminal in the nation comes together every year with all the valuables in transit.
• TRANSPOTATION: The road and train networks to facilitate all this movement of population and goods will be epic indeed. Every city will be a massive hub of trains, roads, and ships. Heavy weapons and cannons will be easily mobilized, and vast numbers of troops and supplies can be shuffled around with amazing speed and efficiency.
• THE RITE OF SPRING: Your social migration will provide a unique pattern to warfare. Your nations are essentially abandoning large amounts of infrastructure every year with no people to hold the significance of a place. Who needs to ethnically cleanse, when you have conveniently vacated the territory you are going to fight over? Every year, there will be a rush to first move troops to forts and borders, and then pour your population in behind them. If an enemy can arrive before your army does, they seize the territory and can hold it, following up with the workers to plant crops, miners to mine mines, and so forth. There will be a strong motive to establish firm border forts staffed in the winter so you can hold your territory and have supplies pre-positioned to allow deployment of your forces as quickly as possible. There will be pressure to open transport lines earlier and earlier, and I suspect there will be a lot of military technological development around covered railways, super-long train tunnels, and early development of train-transported heavy artillery. Blitzkrieg tactics will develop early, as will extensive raiding by cavalry in the initial stages of the war to disable enemy transportation systems.

The take home? Your wars will be fought between armies with logistics trains to put Napoleon to shame. They will be wars of great mobility and rapidly-deployed forces over great distances. Border territories will be swapped back and forth, but the chances of taking a central city with the deep homogeneity of the population around it will be low. On the other hand, if you CAN conquer a city, you can take control or destroy an entire nation's infrastructure. The population will be virtually helpless and used to following directions of a strong central government. But get the people behind you or they can rebel and overthrow the leaders every winter as the entire populous of the country comes together. Destroying their food reserves will kill tens of thousands or millions by famine.

Answer 2

Not really much of a change

Let's take a look at the Franco-Prussian War of 1870, which puts us where your tech range is, and see if anything would have gone differently. Instead of a vast countryside full of small villages, Paris is now double the size. What changes Effectively, nothing. German military strategy during the war relied on quick movements and advanced logistics, something the French didn't have, and used them against the French to great effect.

Railroad networks would of course still exist, as would frontier villages and towns - it's preposterous to assume that they wouldn't. You cannot, after all, effectively collect lumber and coal from the inside of a giant city, so they would have temporary outposts near natural resources and then ship them en masse back to the city, and the outposts would turn into ghost towns come winter, meaning that national supply lines and logistics would remain untouched. Similarly, this would mean that denial of enemy logistics would still exists - Sherman's 'march to the sea' across the ocean in the Civil War (1861-1865) would still be useful, as the Confederates would need to be able to shift good and logistics from ports and plantations down south, though perhaps not as devastating.

If logistics, therefore, remain largely untouched, similarly, battles won't be affected either - urban combat was not a feature of warfare until WWI, in the Franco-Prussian War, you sieged and starved cities. And sieging and starving would still work, because there's only so much food that can be stored, and giant cities do not work well enough to produce as much food as they need.

Answer 3

when winter is that hard food has to be harvested before the first frost and stored in ways that preserve it for long enough that you get to the harvest of the next year.

Cities that are dozens of kilometres across, so 25 km give or take, gives an area (circular) of something like 500 kmˆ2. Looking at a list of cities ordered by land area we see

Taichung Taiwan pop 2,000,000 area 510 density 3,900

Turin Italy pop 1,350,000 area 500 density 2,700

Ottawa/Hull Canada pop 828,000 area 490 density 1,700

from a list of the largest cities

so we could have up to 2 million people in each city. Adults need about 2700 food calories per day which works out to just under 2 billion calories per year. According to this study given the inefficiencies in food production and distribution we can only only feed 6 people per hectare .. so a city of 2 million needs 330k hectares of farmland to feed itself each year, assuming no loss to spoilage. This is 3,330 kmˆ2, seven times the area of the city, which is circle of 65 km.

it is clear that food supply is a significant vulnerability. Given the hardship of attacking during the winter the obvious way to wage war is to spend the summer destroying the food supply of your target city. A siege is not needed .. they will simply die of starvation over the winter and come spring an attacker just needs to show up and take over the empty shell of a once thriving city.

This suggests that blitzkrieg tactics, even kamikaze tactics, aimed at capturing or destroying land under cultivation will be developed, which suggests a heavily mechanised army. And then defensive measures will be developed to block or disrupt such attacks and so the escalation cycle turns into a spiral of destruction.

Note that using machines means having a portable source of power, fuel (IC motors), storage batteries or fuel cells (electric motors), or even nuclear power sources eventually. Any of which further complicates the logistics of it all.

A logical extension will be the development of biological attacks, or perhaps genetically engineered insect plagues, to strike directly at the food supplies as they grow.

Any sort of plague affecting food crops would wreak havoc on all cities in an affected area, making it simple for a city outside of the infected zone to move in and take over, again after a suitable period of starvation to reduce the defenders to helplessness.