2025-09-25 17:23:33
Today I bring you what I think is a ground-breaking article. I have never seen this theory anywhere.1 I hope you find it as exciting as I do!
Societies that live closer to the equator are warmer. Why are they also poorer?
Here’s the average GDP per capita compared to latitude:
And here’s more quantified data:
The debate has raged for centuries with a racist undertone:
Those who live in a cold climate are full of spirit.—Greek philosopher Aristotle, 350 BC.
There are countries where the excess of heat enervates the body and renders men slothful and dispirited.—Montesquieu, The Spirit of Laws, 1750.
As we will see, a lot of the more recent academic research points at worse institutions, laziness, difficulty to sweat, lack of frost, diseases…
But there’s one theory that I haven’t seen anywhere yet, and that I think is crucial to explain the majority of this phenomenon. So today, I’d like to review what people think causes warm countries to be poorer, and then explain why this other factor is so crucial.
In Bali, me and my friends would all go into an idle state without realizing it
You just sit in cafes and restaurants (most don’t have AC there) and doing nothing, just hanging around
Then you’d enter an AC’d cafe (few), and after half an hour you’d wake up from standby mode
You have ideas again, and ambition is back
You wouldn’t even realize you get into this idle slow state but your brain goes on power save mode with the heat and you can’t even think—@levelsio
There is a ton of research that supports this, actually: People are not lazier, they’re just less productive in higher temperatures.
Each additional degree Celsius of temperature (+1ºC) shrinks GDP per capita by 8.5%! Temperature apparently explains 23% of the difference between countries’ GDP per capita.
In poor countries, a 1ºC increase reduces growth by 1.3 percentage points.2
Warmer temperatures decrease agricultural output and industrial output, and make politics unstable!
Within countries, one additional degree Celsius in a municipality reduces GDP by 1.2 to 2%.
+1ºC above 27ºC reduces the productivity of manual labor by 4% (so +10ºC → -35% productivity!)
+1ºC increases absenteeism by 5%!
Hot temperatures make people fail exams.3
A 4ºF temperature increase led to a 10% drop in performance across tests of memory, reaction time and executive functioning.
Politicians speak with lower language complexity when it’s warmer—especially older ones.
Hotter temperatures cause more crime, increase hate speech online, and make traffic tenser. Air conditioning (AC) pays for itself in prisons by reducing fights.
People sleep worse in warmer temperatures.
As I mentioned here, AC has been a crucial tool to develop the US South, and AC is the first thing Lee Kwan Yew implemented when he founded Singapore:
But although temperature might be linked to underdevelopment, what’s the mechanism? Does it make people lazier? Or is there something else?
This fascinating thread explains that warm regions tend to also be more humid.
Humidity makes warm temperatures worse for a few reasons:
Humidity grows mold, which is bad for health
When air is warm, humidity makes it feel even warmer
When humidity is 100%, the air becomes saturated and can’t take in any more, so it’s impossible for humans to cool off through sweat. The only way to cool off is by stopping physical movement.
You can see how warm-climate people might seem lazy: It’s not the people; the climate makes work nearly impossible.
The warmer the country is, the poorer it is, and the unhealthier it is.
But what’s the causality? It’s clear that warmth makes countries poorer, and obviously poorer countries invest less in healthcare and so have more disease. But as we saw in Climate Caused the US Civil War, warmth also reduces health directly, because diseases like malaria, dengue, yellow fever, tuberculosis, or parasitic worms are endemic in these regions: They thrive in warm, humid environments.4
Of course, sick people can’t work, and dead people can’t convey their knowledge to others, so diseases directly make countries poorer. More disease means more children die, and when they do, parents might be more interested in having more children (to diversify their risk) and invest less in each, making each person less productive.
Diseases thrive in warm, humid areas, but they die in frost. 5These researchers claim that frost is good to eliminate pathogens, hence the diseases they cause, with all the economic benefits this provides.
This theory is extremely contested, and I haven’t independently assessed it, so I won’t go into any detail, but for sake of completeness we must add the hypothesis that race also has influence in economic development. I might eventually make an independent assessment of the claim.
This theory goes something like: “Western powers colonized the rest of the world, exploiting its resources and leaving societies in the dirt, while becoming rich off of the spoils. Former colonies are still living the consequences of that.”
This argument is hard to sustain, because:
Some ex-colonies are much richer than others, like the US, Australia, New Zealand, etc.
Some countries reacted much better to Western imperialism than others. Japan became an imperial power itself, for example. China is quite wealthy now.
Some countries were not colonies but are as poor as their colonial neighbors. Ethiopia was occupied by Italy for 5 years only, never truly a colony, and yet it’s one of the poorest countries on Earth. Thailand has never been colonized, but it’s 40% poorer than neighboring Malaysia, a country that’s been a colony for most of its existence.
Meanwhile, hypercolonized regions with very few Westerners are among the richest regions of the world today. Taiwan has been either a jungle or a colony (to Portugal, the Netherlands, Spain, China, and Japan) for most of its history, and yet is one of the richest countries today. Singapore and Hong Kong are very similar: close to the equator, very hot, very few Europeans moved there, yet super rich.
I prefer mechanisms where you can trace the causation more directly, like crops.
We saw this in detail in Climate Caused the US Civil War: Cash crops only grow in the South but require tons of work, so this gave rise to slavery. This locked the South in a much less productive path than the North: Much more investment in slaves, less investment in capital, and the emergence of extractive institutions that were hard to replace with better ones.
The generalization of this argument for the entire world is:
Countries closer to the equator are naturally bountiful
Therefore, they develop extractive institutions, which focus on exploiting people to extract valuable things like cash crops, oil, and minerals.
To add to the problem, these resources inject so much cash into the economy that all prices rise, making other industries too expensive to develop any kind of exports, so other industries wither. These two effects are called the resource curse.6
It’s obvious that institutions matter, like in North Korea vs South Korea, or Haiti vs the Dominican Republic. In both cases, the pairs share the same geography but diverged in institutions for random historic reasons, and the economic differences in outcomes are staggering.
And of course, Europeans colonized many warm countries and left poor institutions behind. It’s easy to see how these can have kept the countries poor.
But the outliers we mentioned before are still valid: The institutions in hypercolonized Australia, New Zealand, Singapore, Hong Kong, and Taiwan are world-class, whereas those in never-colonized Ethiopia and Thailand are bad.7
Also, one of the premises sounds completely off: Are countries closer to the equator actually more bountiful?
Countries close to the equator have famously poor soils, leached by constant rains. The Amazon is impossible to turn into farmland, as are the islands of Borneo and Sumatra. Java is only productive because of volcanoes.
A bit farther from the equator, you find the horse latitudes, which are so dry they create the biggest deserts in the world across every continent.
Meanwhile, the supposedly poorly-endowed US, Canada, China, and Australia are some of the biggest mining countries in the world, and have been for some time.
The US, Canada, Russia, and Norway are some of the biggest producers and exporters of oil and gas.
The US, the Netherlands, Germany and France are the top 4 agricultural exporters in the world.
Acemoglu, Johnson and Robinson (AJR) won a Nobel Prize for proposing a mechanism by which warmer countries could have ended up with worse institutions, which goes back to disease: White people died in warm climates, so they couldn’t send people to properly colonize and develop countries around the equator, so they didn’t care about their development at all, and instead ruled through intermediaries to extract as many resources as possible.
Except Glazer et. al (2004) showed that the difference could simply have been that Europe sent more Europeans to temperate colonies, and their presence made the difference. This could be interpreted as racialism, but there are non-racialist interpretations, like “Europeans simply could transfer institutions more efficiently because they knew them better and knew how they are supposed to work” (a bit like how I believe Americans coming to Europe are more productive than native Europeans today), or “Europeans in the colonies traded more with Europe”. This counter-argument is so strong that the Nobel committee had to caveat their prize.
There are more holes to this theory, such as:
The Scramble for Africa only started in the late 1800s… Because quinine was discovered then and White people subsequently died much less from malaria! Funnily, AJR use Western mortality rates from before Europe actually colonized Africa! By the time Europe was forming African institutions, the mortality rates they used didn’t apply.8
AJR use mortality rates as proxies for institution quality, but mortality rates can also have impacts in other ways, like simply worse health.
They only compare countries with each other, but there aren’t that many countries to compare!9
Plenty of Spaniards settled in Mexico and Colombia 500 years ago, because tropical diseases are much weaker in the highlands, which is where Westerners actually settled. So White Europeans did settle some tropical countries, and yet they supposedly didn’t bring their great institutions.10
More importantly, even if this theory were right, we would be left with this causality:
Bad climate → disease → no Western settlers → bad institutions
Which means the root cause is still geographic.
If you summarize all these theories, this is what you get:
But if you take a step back, isn’t this all so weird? Didn’t humans evolve in Africa? Then how come we’re so maladapted to Africa? How can we not be adapted to the environment we evolved in?
Here’s the kicker—I’m so excited about writing this, I have a huge grin on my face right now: We did not evolve in such warm places, and humans in warm countries don’t live where you think they live!
Here are the temperatures of Nairobi (Kenya’s capital) and Lisbon (Portugal’s):
Lisbon, the capital of the first global empire of the West, actually gets warmer than Nairobi! Nairobi’s temperature is not that high, and is quite stable throughout the year. Look at Mexico’s capital, or Colombia’s capital. Look at La Paz.
The average temperature in many capitals of poor or middle-income countries is not that different from that of some Western countries. Ethiopia’s Addis Ababa is colder than Lisbon, Bogotá is colder than Madrid.
How come? Here’s a map of Italy’s topography and Italy at night. Notice where people live.
Now here’s a map of Colombia’s topography.
Can you guess where people live?
The vast majority of Colombians live in the mountains! More specifically, in the high plateaus. It’s the exact opposite of Italy—and most temperate regions.
The answer is obvious when you think about it: The higher you are, the cooler the temperature. Normally, temperatures decrease by ~4–9ºC every 1000 meters higher (2 to 5 °F/1000 ft). Since Bogotá is at 2,600 m of altitude (8600 ft), its annual temperature is 14ºC (25ºF) cooler than Barranquilla, which is farther north from the equator but at sea level, on the coast.
Bogotá was created far inland in the mountains in 1538, only a few decades after the Spanish discovery of America. The colonizers had a much harder time with disease and conflict in coastal flatlands. It was worth traveling hundreds of miles inland and up thousands of meters to survive. That region is agriculturally much better than the sea-level flatlands too, because of the same lack of disease and the soil that doesn’t get leached as much. This logic is true of all three main Colombian cities: Bogotá (12.7M people), Medellín (4.4M) and Cali (4.2M) are all in the mountains.
We’ve already seen the same phenomenon in Mexico:
Arguably, civilization would have had a much harder time developing in the Americas if the land had been much flatter and low-lying. It’s not a coincidence that the Incan Empire was a mountain empire and was the only independent one in the world to form on the equator!
Even today, the Latin American population concentrates in the Andes!
It is not just LatAm though. Here’s Africa:
Here’s a zoom in on Ethiopia, the 2nd most populated country in Africa:
Here’s Iran:
The pattern is much weaker in East and South Asia:
But if you look at the altitude and distance from the equator of the capitals of the world, a clear pattern emerges:
A big percentage of equatorial population actually lives in mountains:
The closer to the equator, the higher up the capitals! The highest capital of a developed country, Jerusalem, is just 750 m (2,100 ft) above sea level. Meanwhile, capitals of poor countries are very frequently above 1000 m.11
Higher altitude also means less humidity.
Notice how there is much less water vapor in the air in mountainous areas than close to sea level. This other dew point map is not as pretty, but shows directly how the dew point is lower in mountains.
So in tropical areas, sweat doesn’t work to cool skin on sea-level plains but still works in the mountains.
So the trend is clear that, closer to the equator, people tend to live in higher altitudes. What are the consequences of that? If you follow Uncharted Territories, you should already have a sense.
Mountains mean people need to travel up and down mountain passes and huge slopes to get anywhere. They mean no navigable rivers. They mean much higher costs of infrastructure, so there’s much less of it. This means transportation costs are much higher.
This, in turn, means there’s dramatically less trade, and so less money is made, and less wealth accumulated. We’ve seen how these facts have dramatically impoverished countries like Mexico and Brazil, and the generic process in A Science of Cities.
The other thing that happens with mountains is conflict. As transportation costs are so much higher, people don’t move as much from their valley. There’s substantially less regional integration, and people trust and like each other less. They develop their own independent customs and mistrust those of their neighbors. This leads to more conflict between valleys, regions, and countries.
This process is called Balkanization, for the mountainous Balkans in Europe. But we also see it in Mexico’s and Colombia’s cartels—in fact, nearly all cartels in Latin America are in the mountains. We saw it in Iran, a highly mountainous country that requires a very strong state suppressing dissent to keep the country together. It is extremely obvious in Africa:
And… where did humans evolve?
The pattern, and its logic, is unmistakable:
Humans evolved in the African highlands, where temperatures are stable throughout the year, and close to that of spring & fall in temperate regions. This is why we feel most comfortable there.
Close to the equator, if we’re not in the mountains, the temperatures are too high for us. We can’t think or work properly because we overheat, and our sweat can’t cool us off because humidity is too high.
We also suffer from many more diseases, more common in hot moist climates, but also because we didn’t evolve there.
This also affects food, as agriculture is much harder in these hot moist climates, given the pests, the speed of rot, and the work required by crops.
This prevented maladapted Westerners from efficiently transferring culture and institutions to these hot, humid, low-lying areas, yet another way these regions suffered.
In order to avoid all that, people close to the equator tend to live higher up, in mountains, where temperatures are cooler and the dew point is lower, allowing people to cool down with sweat when necessary.
The big tradeoff for this comfort though has been much higher transportation costs, so less trade, so less wealth.
This also leads to much more ethnic diversity.
This diversity breeds conflict, which makes everybody poorer.
Ethnic diversity and conflict also mean institutions are much harder to make and keep.
This is how mountains are the most significant underdiscussed topic in economic development, and how they must be considered to better explain why warmer countries are poorer.
So people in warm countries could pick their poison: Either be on the lowlands with lower productivity and more disease, or move to highlands with less trade and more conflict. Most of LatAm and a big chunk of Africa gravitated towards the highlands type of poverty, while East and South Asia gravitated towards the lowlands type.
This is also why one of the most important inventions in the history of alleviating poverty is air conditioning, and why all low-lying warm countries should obsess about solar energy and electrification, to power AC to increase productivity and reduce diseases.12
Why does all this matter though?
Because I’m tired of worthless debates like who is guilty of poor countries’ misfortunes? where one side claims “Oh the Western colonizers caused all the problems” and the other argues “Actually, the colonizers saved shithole countries from their shit”. Neither are useful because they’re not actionable. They focus on blame rather than on analyzing the root cause that we can do something about. If it’s true that mountains have had such a major impact on poor countries’ poverty, that clearly points at a path for their development:
In low-lying areas: Populate them with more AC and focus on eradicating diseases, especially via the elimination of mosquitoes and stagnant water.
In mountainous areas: Invest heavily in transportation infrastructure.
I asked ChatGPT and Grok about it and they agreed. I will share the links later so as not to spoil this for you!
This is huge! If your country grows at 3% per year and one year the average temperatures are 2ºC higher, growth will fall to 0.4%, or 85% less growth!
“Hot temperature reduces performance by up to 13 percent of a standard deviation and leads to persistent impacts on high school graduation status, despite compensatory responses by teachers, who selectively upward manipulate grades after hotter exams.”
Even this has an indirect relationship with economics, as rich countries have been able to eradicate malaria in a way that poor countries have not, because these diseases are easier to eliminate in colder climates, and with higher investments.
Diseases that spread in cold temperatures don’t do so because they thrive in the cold (they don’t, they die). Rather, they thrive in humans’ lungs, throats and mouths, and love the indoors. So when it’s cold, people stay indoors, and spread the virus from respiratory system to respiratory system. That’s why they’re called “cold” when they don’t like it.
Or Dutch Disease, after the Dutch discovered natural gas in the 1970s and the economy suffered from it. Spain is also a perfect example, where the vast sums of silver from America might have completely destroyed its industries for centuries.
I’ve also heard some countries inherited reasonably good institutions, like Namibia from Germany, but I haven’t looked at it independently in any detail.
Also, these mortality rates were linked to military campaigns, not civilian settlement. Many of the observations were from just one instance.
They used about 60, and the max I’ve seen is about 140. This is a fair share of countries (~196) but there are just so few countries in the world that it makes it hard to reach significance just comparing countries.
At this point, AJR argue that Spanish institutions were just not great to begin with, and explain how they just replaced extractive institutions that existed before they arrived. But then why were Spanish institutions so bad compared to English ones? And why did the English ones suddenly become bad institutions in the South of the US but not in its North?
Ulaanbaatar, in Mongolia, is extremely high for its latitude, which is why it’s the coldest capital on Earth. La Vella, the capital of Andorra, is higher than Jerusalem or Madrid, but Andorra is a microcountry that is only rich because it’s nested between France and Spain.
2025-09-24 20:02:52
All the principles we’ve seen in the previous two articles shape how to make a city great. Adding a couple more can tell us an inordinate amount on how to make cities amazing to live in.
Transportation costs are paramount. Cities must do everything they can to minimize them.
This is especially true for the main transportation …
2025-09-19 22:02:58
In our previous article, A Science of Cities, we uncovered the big forces that determine population density, how people gathered in villages, and how some of those villages grew more than others. These forces are food productivity, agglomeration effects, and transportation costs. Today, we’re going to see how these forces, plus a few more, determined which cities grew and which ones remained small. Next, we are going to see how cities are structured inside.
The regional productivity of the land will determine the average population density: The more fertile the land is, and the better the technology to extract food out of it, the more food will be available and the more the population will grow. As we saw in Pax Mercatus, inventions like the heavy plow, the horse collar, horseshoes, and horse breeding brought an agricultural revolution to Northern Europe that exploded local population, and that led to the emergence of cities.
The number of people who can live in cities will be determined by the food surplus. For example, if every person can only produce enough food to feed themselves, everybody will be a farmer. But if every farmer only uses half of their harvest, the other half can feed non-farmers, and so 50% of the population will be able to do other work, usually better done in cities. In other words, the food production surplus determines the share of urban population, up to about 80% city dwellers.1
But how does this food reach the cities? In A Connected Place, we discussed how cities were realistically structured:
Notice how there’s plenty of farmland inside the city walls. Outside the walls there was more.
We saw in that article that the simplified model was this:
The food that must be consumed soon after production had to be produced within the city or close by.
Some forest land had to be close by too, because wood is heavy, so transporting it is expensive.
Farther out, grains, since they don’t spoil. They can be transported slowly and don’t need refrigeration.
Farther still, ranching, as cattle can move by foot.2
In this structure, farmers in the periphery sell their grain surplus to the city, which is one of the reasons that surrounding villages can’t be too big: They must produce a heavy surplus to feed the city, so they can’t have too many hands per farm.
But as we discussed, transportation costs had a prominent role: They were so high that they could quickly make any product prohibitively expensive. And as you might know by now if you read Uncharted Territories frequently, river transportation costs could be 10-30x cheaper than overland.
The easier the river transportation, the faster boats could travel and bring food from faraway villages. This is why Ancient Egypt’s capitals were so rich, harvesting all the farming surplus of the entire Nile.
This is why all the earliest civilizations emerged along rivers, first as cities, which then conquered or allied with more and more land and other settlements along the same rivers.
One way to get a sense of this is through “isochrones”:
The confluence of rivers increased the influence area.
And this is also why rivers were better than coasts.
At a macro level, coastal cities allowed the emergence of big empires (and thus huge capitals). This is why the Roman Empire was called Roman (from the city of Rome) and why both Rome and its empire were so big: The Romans used the Mediterranean (Mare Nostrum, “our sea”) as a highway to transport grain from across the empire (notably Egypt). Its roads had the same effect.
Why gather in cities though? We mentioned in the previous article why people bundled in villages, but why get together into bigger groups?
There’s a clue in the paintings of Padova and London I showed before.
Of all the existing cities I know that were formed centuries ago, virtually all of them are in a highly defensible spot:
London was on a hill on the Thames. Other cities along a river with a fort on a hill include Athens, Carcassonne, Salzburg, Budapest, Prague…
Byzantium / Constantinople is at the end of a rocky peninsula, like San Francisco.
Pittsburgh and Lyon are on a hill at the confluence of two rivers.
Cairo (and all of Egypt) are protected on three sides by desert, and by sea on the 4th. The same was true of the early Indus Valley civilization..
Mexico was on a lake surrounded by mountains
Rome was on hills close to the Tiber river, in a marshy and malaria-prone area
Moscow was ideally suited to defend against the steppe hordes.
Many of the cities we know today in Europe and around the Mediterranean were founded by Romans first as military bases, and only after did they become cities. This suggests the more general mechanism:
Villages were attacked by neighbors or foreigners
They would pack into bigger towns to wall them and protect themselves3
Those towns that could protect themselves the best were more likely to survive and attracted more people, eventually emerging as big cities
Many of these cities were on rivers because of the protection, the water for drinking, for irrigation, to source food from farms along the river… And from trade.
In Why Some Cities Thrive, we covered the main mechanisms of how ancient cities grew:
They tended to start as military centers
Which transformed them into administrative centers
For protection, food, water (drinking and irrigation), and transportation speed, they tended to be on rivers
The ones that were on the best parts of rivers (navigable waters at the confluence of rivers or at their mouth) grew much faster than the others
In other words, the key factor that made a city grow a lot was being at the crossroads of cheap transportation lines. We see this in virtually all the cities I’ve covered.
So the ideal city is a village that happens to be on the confluence of several calm, navigable rivers, on an estuary close to the coast, with a ford to cross the rivers, and near a natural road that connects important points.
What’s a natural road? A line that quickly connects one important city to another through pretty flat terrain. You can see for example how many of Spain’s modern roads are close to where old Roman roads were:
Locations at line crossings evolved into marketplaces, which generated wealth that could pay for the grain and infrastructure needed to continue feeding them.
I explained how valuable rivers were for this process in Starship Will Change Humanity Soon:
Imagine you sell meat and can make a profit of $10 for each kilogram you sell. But it costs you $1 to transport each kg one kilometer. Each additional kilometer you add, your margin is reduced by $1. You can only transport your product 10 km away. In the example below, that means you can only trade with four cities:
If instead, your cost of transportation is half of that, what happens? It costs you $0.5 per km. Now you’re increasing your margins with each of the cities that you trade with. But more importantly, now you can reach markets that are 20 km away.
But when you 2x the distance, you 4x the surface! In this case, you can’t just trade with four cities anymore, you can trade with sixteen2! But according to Metcalfe’s law, the value of a network grows with the square of its nodes. Because now it’s not just your city that can connect to these sixteen other cities. Each one of these cities now can connect with sixteen other cities! All of them become richer, which means they, too, can now buy more meat.
This is what rivers do: By dropping the cost of transport, they connect huge numbers of cities, which can trade much more between them, become wealthier, their population can buy even more, and so on and so forth.
All in all, the value of the network to the right is at least an order of magnitude higher than that to the left! The cheaper the transport, the more trade at a lower cost, the more wealth generated, the more that wealth can be reinvested in better canals and bridges and roads, and the area’s wealth grows even further.
To use a concrete example, imagine the costs of $1 of woolen cloth. $0.30 could have been for getting the wool, $0.30 for converting it into cloth, and $0.40 for transportation. Let’s assume that, to make a profit, it is sold for $1.20. Of the $0.20 of profit, $0.15 goes toward the trader’s living costs, so he can save $0.05.
Now halve the transportation cost. Suddenly, the average profit rises to $0.40, and after living costs, the trader can save $0.25, or 5x more than before!4
But as we have seen, this also expands the market. Now the trader can cover 4x the area, so he will be able to sell 4x more cloth, so he will make $1 where before he was only making $0.05! Of course, this also increases by 4 the amount of wool production.
Or maybe more, because competition will bring prices down, which will increase demand. This competition emerges because more people see a profit to be made in wool trade. And they will sell their product wherever someone else is already selling it—to benefit from existing customers. The added variety will attract new customers, who will attract more sellers.
Soon, dyers will also come to dye the cloth with beautiful colors. Designers will innovate the cuts. Weavers will start co-locating in the same city, because that way they can see what sells, and they can make those types of clothes. Button makers will also settle nearby, to sell their buttons to clothmakers. Boats will specialize in carrying wool and cloth, making that trade more efficient. Soon, you have an entire industry that co-locates into the same city because of the economies of agglomeration.
2025-09-17 03:45:23
I have written over 30 articles on cities, and from this a pattern has emerged: It seems to me that the emergence of cities and their optimization can be treated a bit like physics, like a deterministic science.1 I have seen bits and pieces of evidence for this across the Internet, but nothing holistic. That’s what I want to do in this series, with an overview of three big points:
How did cities emerge? (this article)
How did cities grow?
What makes a city better?
Historically, the biggest driver of the number of people that could live in a specific area—the density of people—was food per acre:2 If one acre can produce a lot of food, it can feed lots of mouths, and lots of people will live there. Less productive land will not feed as many people, so population density will be lower.
This has been true since forever. As hunter-gatherers, we could only survive if there was enough food around. This usually meant game (hunter) and fruit (gatherers). In other words, calories.3
Places with few calories available, like mountains or deserts, couldn’t host many people. Instead, they concentrated where these resources were most naturally abundant: tropical forests, coasts, riversides, and estuaries. This is why the bountiful US Pacific Northwest could sustain more than 50 ppl/km2 thanks to its whales, salmon, and other resources, while the more hostile Amazon Rainforest can only sustain 0.2 humans per km2, and Arctic regions as low as 0.002 ppl/km2.
The same rule was valid once humans developed agriculture over the last 10k years or so. But how many people could fit in one place with agriculture?
More people can produce more food from a farm, up to a certain point.
More people don’t mean more food production, but they do mean more food consumption.
The balance between production and consumption will determine the size of a village.
Let’s take the baseline of 2000 calories per person per day. This means a person needs to consume approximately that amount every day of a year to survive, so 730k calories per year from harvests.4 Then, you have to keep some of the harvest to replant the following year, plus there’s some storage and spoilage. All in all, let’s say ancient societies needed 1M calories per year to sustain one person.5
How many calories could an acre produce? It varies a lot, but ChatGPT, Claude, and Grok tell me from ~0.6M per acre in Medieval England, to 1.5M in Rome, and 3M of rice in China. This means that England could feed 0.6 people per acre at most (about 150 people per km2), while China could feed 3 people per acre (750 ppl/km2), and Rome 1.5 (375 ppl/km2).6
Of course, that’s a maximum. Not all land was cultivated, some calories came from other sources like meat, fish, vegetables, or dairy, etc. But this gives us a ballpark of how things worked.
It also tells us something about the mechanics at work in societies at the time. For example, a household had ~5 people,7 which means the bare minimum farm size for a household ranged from less than 2 acres in China (6M calories produced per year) to 4 acres in Ancient Rome and 8 acres in Medieval England (4.8M calories produced per year).
What this tells us is that the population density of one area was the result of two forces:
Soil quality
Technology8
Soil quality was normally highest around volcanoes and close to rivers, thanks to the sediments each one brought and the natural irrigation of rivers and mountains.
Humans could have an influence using technology: clearing forests, irrigating, using manure, improving plows, selecting the best grains to replant, harvest after harvest…
This means the carrying capacity of a piece of land was determined basically by the luck of local soil quality, and by the evolution of human ingenuity, which could produce more from that soil.
Now we know how many people can live on a piece of land, but not how they distribute themselves.
Anybody who has lived in a village knows why they exist:
When harvest time comes, households can help each other, and that’s crucial because farm work is highly seasonal: Some weeks have no work, other weeks it’s all hands on deck.
More households hedge risks: If somebody gets sick, the neighbor can tend to them. If one has a bad harvest, the other can share their crop.
Infrastructure is expensive: A single person can hardly build a granary, a mill, a road, a bridge, an irrigation system… When groups get together, they can share these costs.
If you’re alone and a foreigner attacks you, you are cooked. But if you stand together, you are more likely to fend off invaders.
So most people didn’t live alone, and bundled together instead. This has been true of all humans since we were hunter-gatherers.
If people benefit from living together, what’s the maximum size of a village?
Marchetti noticed that city sizes in antiquity were limited to ~30 minutes of walking distance from end to end. The intuition behind that is that people would not want to walk more than 30 min each way to go to work. This then carried through to more modern transportation systems: Trains and cars allowed these 30 min to take you farther, thus growing cities.
If this is true, it probably applied in the past, too, so people wouldn’t want their farms to be much farther than 30 min walking distance from the village. Otherwise, they would just create or join another hamlet.
Since human walking speed is about 4 km/h, in 30 min a person could walk 2 km. This limited how far a village reached: A 2 km distance means about 3,000 acres,9 which would fit ~375 farms / households maximum (~1800 people) in Medieval England, and 1500 households (~7,500 people) in China.
This is why the largest ancient towns hosted at most a few thousand people.10
Note that this is the maximum size of a village, one that would consume everything it produces and would die off in bad harvest years. One where people would be crammed in their households and had only small plots to farm. One where most fields were so far away from the house that the farmer could only see one of them each day, and would waste a ton of time walking there.
Logically, this was not what happened in most cases.
Most villages in history actually had 150-300 people.
Instead of having big villages every 4 km,11 it would make sense to be closer to the fields, so there would be more small villages, closer together. I took a random sample from India and found the distance between villages is about half that today.
In China, it’s about 500m!
But this sample from Ancient Greece shows the distance between villages was 5km!
Of course, the soil of China’s heartland is much more productive than Greece’s. The more food, the more population density. But why did this translate into more small villages rather than bigger villages?
Imagine you’re an Ancient Roman with an 8 acre farm and five children who survived to adulthood, two daughters and three sons. Normally, the sons inherited the land, but if you divide your land in three, each son will get only 2.7 acres—not enough to feed them and their families! Even dividing it between two sons will still give them only 4 acres each, which is not far from subsistence level. Dangerous: Mortality was very high at the time, and a bad harvest could mean much less to eat for everybody. Young, healthy people could survive, but very small children and old people would be weakened, and any infection could kill them. People wanted to avoid getting close to that point.
So the farm owner might want to keep his farm in one piece and give it to the eldest son. But then the other two sons will remain farmless. What will they do?
Whenever a village would become too crowded, people would just leave and settle some more land. In the Neolithic, or in the Dark Ages, that could have meant clearing some adjoining forest. But in Roman times, it meant enlisting in the army to go kill some neighboring peoples, take their land, and farm it yourself. Indeed, citizenship and land was the pension, the final prize of having served the army for years or decades.
Another factor is that not everybody was a farmer who worked on their fields. The lords and their entourage had large estates, but they were not the ones to work on them—the other farmers were. The surplus from their work was dedicated to feeding nobles, along with any other person who didn’t farm directly—mostly warriors, clergy, merchants, artisans, and other townspeople.12
So now we have the main drivers of village emergence:
Food productivity determined the population density of the land.
Farming increased the food productivity of the land, so it increased the population density.
Agglomeration effects pushed people to live together.
The size of a village was capped to a few hundred to a few thousand people because of the transportation costs of walking.
People tended to leave their villages before the cap was reached and they became overcrowded. This usually meant either clearing new fields and settling nearby, or joining armies to conquer new farmland.
How do we go from village to cities? And how do you actually organize cities to make them great?
Christopher Alexander’s A Pattern Language is an amazing book that tries to do something similar, but is much more ambitious (it goes from the ideal size of states to the ideal types of chairs around your dinner table), and more intuitive. I intuit that urbanism should be a much more scientifically precise science than it currently seems to be, given how terrible most new urban landscapes are.
More precisely, calories per unit of land, but that’s harder to understand, so to introduce the concept, let’s keep it simple.
Technically, kilocalories, but everybody calls them calories. I’m confused about this.
This is an average. Let’s assume most calories come from grain, which I believe is reasonable for our math. Also, apparently, humans need a bit more than 2000 calories per day.
It looks like about 10% of harvests were dedicated to reseeding and 10% to spoilage, which means a total of 910k calories per person would be needed. Also, not all the calories produced were consumed (eg the plant stems are not edible). And there was also usually a 10% or so tax, bringing the total to 1M calories harvested per farmer. But farmers are producers, not consumers. The tax was dedicated to feeding non farmers. So the number is probably around 900k per person, but for rounding goals I’ll use 1M. The 10% spoilage for grain comes from Medieval England. It’s 20% in extreme situations in Africa today. The reseeding seems to have reached 25% in the Middle Ages. In Rome, apparently it was around 10%.
I’m simplifying here and making assumptions, but I’m trying to get to the simplest model to expose how things have probably worked.
A typical size was 6-7 people, but there were also a bunch that had only a few or just one, so the average turned out to be ~5.
In the broadest sense, this includes better crops, crop rotation, better institutions, better ideas on how to sow, till, harvest…
The surface is π*r2=π*22=12.5 km2. Since one km2 fits about 250 acres, that’s 3,125 acres
According to Claude, Grok, and ChatGPT. I spot-checked them and they seemed correct.
2 km to go from one village to the Marchetti limit, and another 2 km to go from that limit to the next village.
This doesn’t change the fact that the amount of food per acre was the main determinant of total population density. Put another way, if say 70% of workers were farmers, and 30% did other things, the 70% worked the farms that fed the 100%. Those farms, and their production, was the limiting factor for the entire population, since farmers could work on more than just their own farm.
2025-09-12 23:20:17
160 years after the end of the Civil War, the US South is more poor, sick, uneducated, mentally distressed, crime-prone, incarcerated, unemployed, religious, socially disconnected… Why? Is it a consequence of the Civil War, or something else?
In the first article in this series, we saw how climate caused the US Civil War. In the second, how climate also meant the North was more developed, setting it up to it to win the war. We are still experiencing the consequences of that clash today.
For decades, the North spent its capital building railroads, trains, canals, ships, machines, cities, industries… It automated farm work, which allowed laborers to leave the farm and go to the city, where they worked in industries and benefited from cities’ agglomeration effects: Indeed, cities generate more money per person than farmland.
Meanwhile, the South invested all that capital in buying slaves.1
From Climate Predetermined the Outcome of the US Civil War:
40% of Southern wealth was locked in slaves around 1860, and their value exceeded the invested value of all US railroads, factories, and banks combined!
So, very early on, the North and South diverged: The North developed an industrialized economy, while the South went down the path of a resource extraction economy (extracting value from slaves). A bit like a European vs a Caribbean economy. These trajectories take incredible amounts of time to curb, which is one reason why nearly every European country today is richer than nearly every Caribbean country.
Then, the War tore down the South, destroying what little industry it had. Between government spending, physical destruction, loss of human capital, decline in consumption, emancipation, and the effect on cotton prices, the Civil War was over 4x more destructive for the South than the North.
Once it ended, all the capital locked into slaves vanished. Of course this was the right outcome: In effect, it meant ex-slaves would no longer be abused as much, and that they had to be paid fair wages. Financially though, it meant that the upfront, fixed capital to secure years of practically unpaid work2 had vanished, and instead, workers had to be paid a monthly, variable amount.
This also destroyed the profits of Southern plantations. Many became unprofitable and closed. This was beneficial in the long term, because more productive enterprises could take over the worst ones. But in the short term, it meant a financial shock for the South.
When we looked at Asia’s development, we saw that the first step was always land reform, so that farmers owned their land and the fruit of their work. This usually meant that the winners of the war obliterated the incumbent establishment: This happened in Japan, South Korea, and Taiwan. Alas, the plan to allocate land to freed slaves in the US South was reversed after Lincoln was shot and Andrew Johnson became US President.
Instead, sharecropping appeared: White plantation owners still owned most of the land, which laborers would farm in exchange for a share of the crop. The drawback was that, between the land, the fertilizer, the seeds, the machinery, and all other things laborers needed, they ended up keeping very little of the fruits of their work. One of the reasons was that they didn’t know the system well, so plantation owners would take advantage of them and keep most of the benefits. And the natural trend of land ownership is toward more concentration anyway, since after every bad harvest, small landowners would have to sell their land to bigger owners that had more of a buffer. In effect, all this maintained the former slaveowners’ rentier status.3
This was not the only way this aristocracy of landowners was maintained: By disenfranchising former slaves (and poor Whites), the Southern White Elite prevented them from voting, so it controlled the politics of the US South for decades after the Civil War. This control turned the system to their advantage. For example:
Prisoners (mostly Black) were de facto slaves, used as plantation workers.
Anti-enticement laws prevented laborers from finding the best employer.
The controlling Elite kept taxes low (they would have been the ones taxed) and thus didn’t invest in infrastructure for the region.
Jim Crow Laws maintained segregation in the South, making access to services like healthcare or education nearly impossible for Blacks.
Unsurprisingly, Blacks eventually decided to leave.
Most Blacks remained in the South after the Civil War, as they didn’t have many options outside it, nor connections or savings to get them out. This changed in the early 20th century.
WW1 was especially beneficial for Blacks in that it offered incredible professional opportunities:
Lots of Northern workers had to support the war effort, through both the war industries and military service in Europe.
European immigration dropped by 75% between 1914 and 1915.
Wages in the North could be 2x those in the South, so Blacks moved there en masse.
The Great Migration started around 1910 and lasted until the 1970s.
The result is that the Black share of population in the South halved!
This had several effects on the respective economies of North and South:
The South’s economy shrunk proportionately to the number of Black people it lost.
The North’s economy benefited from more workers.
Most newcomers went to cities, where they were more productive than on farmland, thus further enriching the local economy.
So now, the South suffered, on top of everything else, a loss of population and workers. And as a result, wages had to rise to attract other workers, further compressing the profits of local companies and causing inflation.
Of course, we should add to all these problems the endemic malaria, yellow fever, and hookworm we discussed in Climate Caused the US Civil War.
The result of all these factors was that the South’s economy stayed weak and small for decades after the Civil War.
In summary, climate caused the economic divergence of North vs South, it caused the Civil War, it made the South lose the War, and for a century afterwards, the South was unable to reverse the resulting economic depression. Luckily, over the last few decades, it has.
2025-09-10 18:31:03
We covered why the US’s geography is so overpowered in the previous article. How does it compare to China?
Both have a continent-scale country surrounded by oceans and mountains, with a massive heartland plain, criss-crossed by rivers that make it highly fertile. But when you get into the details, the differences become stark.
For starters, China and the US are broadly similar in size:
Both are continent-sized superpowers.
China’s east and west are protected by the sea. The rest is protected by a series of mountains:
Most of China’s border with India is protected by Tibet, the most elevated plateau in the world, which ends in the Himalayas, the tallest mountain range in the world. Absolutely impassable. This is very much why China annexed Tibet in 1951, in a move quite similar to how the US co-opted Texas in the mid 1800s to protect against Mexico.
If that wasn’t enough, there are also the states of Nepal and Bhutan that serve as buffers between them—which India and China fight to co-opt:
The southern part, the border between China and Vietnam / Laos / Thailand / Myanmar, also has mountains, but they include another barrier: some of the densest jungle in the world.
To the west, Xinjiang is big, mountainous, and desertic.
This is what it looks like:
To its north, it has lower mountains but also steppes that are sparsely populated. Farther north, the even less populated Siberia:
To give you orders of magnitude, Mongolia has just 3.5M people, to China’s ~1,400M.
As we discussed in Putin’s Mindset on Russia, if anyone is going to do some invading here, it’s China in Siberia, not the other way around.
Finally, the only land border it has to its east is with North Korea, a vassal state.
You can see the parallels with the US:
Continent-sized
Seas, mountains, and deserts protecting its borders
In addition, it has buffer states to protect it (Bhutan, Nepal, Mongolia, North Korea, and in Central Asia it has influence over the Central Asian republics).
But when you get into the details, you can see how much flimsier China’s protections are compared to the US’s.
There are many, starting with the seas.
China’s coast is so littered with enemies aligned with the US that we can call them a sea barrier. China can’t actually access the Pacific Ocean without passing one of these barriers. If the US really wanted, it could choke China’s passage here.
And this is not theoretical: Western powers arrived in China from the sea in the 1800s and triggered the Opium Wars:
They subdued China, kick-starting its century of humiliation.
Japan followed Western Powers, and conquered a huge chunk of China:
Later, the US supported South Korea’s independence from North Korea through naval operations.1
All of this to say: China might have a big coast, but it’s nothing like the US’s Pacific and Atlantic Coasts, which are completely safe from seaborne threats.
To its south, Vietnam is somewhat comparable to Mexico. Their populations are 100M and 130M respectively, and most of the border is impassable. But unlike the Mexico–US border, the Vietnam–China border has a huge opening.
Northern Vietnam is basically the Red River Basin. That basin has an opening to China that is only a few hundred feet / meters high. That border has jungle, but it’s reasonably well populated and built out too, making logistics quite easy.
This is why China has invaded Vietnam maybe a dozen times2 in its history, the last one just 50 years ago. If invasions go in one direction, they generally can go in the other. And yet Vietnam has proven it can’t be easily conquered. It could not invade China, but it could definitely hurt it if an international armed conflict emerged in the region.
If you go to the west, of course there’s India, the most populated country in the world. Thankfully for both countries, they’re protected from each other by the Himalayas and Tibet, but still, this proximity of two behemoths is not a very stable situation.
If it were only India, maybe it could be manageable. But China is the country with the most neighbors!3 And most of them are on the western border: Vietnam, Laos, Burma, India, Bhutan, Nepal, Pakistan, Afghanistan, Tajikistan, Kyrgyzstan, and Kazakhstan.
China’s enemies only need to co-opt a few of these Chinese neighbors to make China nervous. The result is that China needs to constantly manage a host of them to make sure they don’t turn against it. And of course, this is not easy work since this is the most populated region in the world.
Continuing our clockwise trip, the western parts of China might have deserts and mountains, but the Silk Road was still able to cross this region.
There are several passes that allow for people (and hence the military) to cross this.
China knows this, and it’s why it has continuously expanded westward, to create as big a buffer as it can. This is why it has worked so hard in history to conquer this region:
It’s also why it has recently worked to sinicize Xinjiang. The buffer in this region is now large enough to protect China, but not because it’s impassable; because it’s big.
And then there’s the north. It is not a huge threat today, but the existence of the Great Wall of China illustrates how this was no pacific region in the past.
On the map:
Mongols attacked China hundreds of times, with maybe a dozen real invasions, half of which were successful! These include Genghis Khan’s invasion, and the Manchurian one, which deposed the Ming and became the last Chinese Dynasty, the Qing. Mongolia doesn’t have the power to do this anymore, but Russia is another matter.
All this shows that, unlike the US, China is in a much more precarious position defensively speaking.
Like the US, China has a very productive heartland.
