Suppose you’re writing a story that involves trade between cities, or maybe between a city and a rural area. Maybe your protagonist is a merchant, or a farmer selling goods in the marketplace, or the Lord Mayor. So you’d better have at least some concept for how a city economy works, and how cities interact with their surrounding regions. There is much to say about the topic, of course; Fernand Braudel (for one) wrote three massive books on cities and capitalist economies. But you’re not writing an economics textbook; you just want a simple yet powerful model to sketch out some background for your story. If so, you’re in luck. I love simple and powerful models, and here’s a good one.

Writing in the 1980s, the pioneering student of cities Jane Jacobs produced a short, scintillating book that should have been like a torpedo into the waterline of conventional economics, Cities and the Wealth of Nations. She argued that most national economic policy was wrongheaded, because it focused on economic activity at the national level, rather than at the level of the fundamental unit of economic activity: the city. Globalized supply chains of the type we are familiar with, on the other hand, don’t tend to produce regional prosperity, because they don’t generate complementary webs of economic activity in the places that feature nodes of the supply chain.

Needless to say, Jacobs’ work has not been popular among the business class or conventional economists. And many of her arguments get complicated by the radical decentralization of the internet. Still, especially for authors writing about pre-internet societies, Jacobs’ work provides a useful set of tools for understanding complex economic effects. If you want to feature economic change as a major contributor to your plot, read on.

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Jacobs argued that the main way that a city can generate sustainable prosperity is by developing local industries that produce things that the city formerly imported. This allows the city to internalize the profits that formerly went to the trade partners. But more importantly, it allows the city to develop webs of technical expertise and complementary industries, which it can then build on to grow related industries and replace more complex imports, and so on.

Meanwhile, the city does not import any less than it once did; it may in fact import more as it grows wealthier. But it does import different things than before (including innovative goods produced by other cities), raising its material standard of living. Imports thus play three roles: they are consumed; they are the earnings of successful economic development, and thus stimulate that development; and they are candidates for local replacement. (This makes them different, and more economically potent, than simply throwing money at a city in order to magically produce economic growth.)

(This echoes our discussion of energy surpluses as the spur to material and cultural development.)

As the city replaces imports, it exerts five kinds of forces on surrounding regions:

• Enlarged markets for new goods from rural regions or other cities;
• Increasing numbers and kinds of jobs in the import-replacing city;
• Displacement of former city industries into surrounding rural areas;
• New uses of technology, especially to increase rural productivity; and
• Growth of city capital.

When these five forces are in balance, they tend to make the surrounding region more prosperous as well, anchoring a general growth in wealth and human flourishing. That is, a balanced city turns its hinterland into a city region. A city region benefits from the increased economic activity of the city, but is not distorted by it; it still produces more for its own use than for export to the city. But the availability of city markets for rural goods, city jobs for people who lack employment at home, and new industries spilling out from the city, along with new productive technology and the money to pay for its use, make the city region thrive.

The five forces often do not act equally, however. When one or two of the forces acts with disproportionate power on a given region, the region becomes distorted in characteristic ways.

A stagnant region, for example, features widespread poverty, a sluggish economy, and a low level of technology. If a nearby city becomes more prosperous, the stagnant region does not benefit. It cannot produce much that the city needs, and for whatever reason cannot support the industries that are being displaced from the city. What does happen is that the most productive and adventurous people living in the stagnant region pull up stakes, and move to the city to work. The stagnant region, already in a desperate state, becomes hollowed out as its workers leave. If workers send remittances home, that can help improve the standard of living of those still there; but only by funding current consumption. Such remittances don’t tend to generate local industries and economic growth, because the stagnant region cannot support new businesses or work the way that the city can.

In a clearance region, on the other hand, new technology makes production more efficient, displacing some of the existing workforce, but few or no new jobs are forthcoming. Many people are driven from the land or from their previous jobs, and they suffer as a result. The ones who are able to stay, on the other hand, benefit from the new technology and their improved productivity. For example, in the 1970s, India, seeking to improve conditions for the rural poor, sponsored the development of a bicycle-powered spinning wheel. Using it, a villager could produce as much yarn as twelve workers using traditional spinning wheels. However, the other eleven villagers, who had spent their whole lives spinning wool, had no other work to do; the new spinning wheel simply made them destitute, even as the first worker benefited. So India could not dare to encourage the use of the labor-saving device it sponsored.

If growing city capital and growing city markets combine in an unbalanced search for raw materials, a region can be transformed into a supply region, where economic activity is dominated by the extraction and transport of raw materials for export (like timber, iron, or coal). Without new local industries to balance out the economic effects of the city’s inexorable need for raw materials, most workers in the supply region will depend on supplying the one thing that the city wants. Extractive activity doesn’t tend to generate new webs of productive or commercial expertise in the supply region; the region instead goes through unproductive booms and busts as its main resource becomes more or less valuable. This is the “banana republic,” the “oil town,” where momentary wealth goes into expensive imports from the outside world that do not generate sustainable prosperity in the region itself. (Partly due to the “Dutch Disease” or “Resource Curse,” which I hope to discuss in a later post.) If the supply region is particularly unfortunate, its populace may even be enslaved by the armies of the cities that need its resources. The Congo Free State was a particularly tragic example.

Finally, some regions are lucky enough (or so they think) to attract an economic transplant. These are large factories belonging to huge companies trying to create a regional, national, or even global supply chain. However, transplant factories are not integrated into the local economy, but are like self-contained bubbles of productive capital, parachuted from the sky. Unlike factories that emerge organically in a city or city region, the transplant factory might employ local workers but does not depend on local support industries and so does not generate complementary economic activity or technological development. Specialized equipment and the technicians who get it working are flown in from the company’s home base; production inputs might come from another country, or several other countries; and the local workers don’t tend to learn transferable skills. Even though local governments often compete furiously to attract such transplants, they rarely end up generating broad growth as the governments hope.

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Now, Jacobs’ theory predated the internet, and even when it was written it had detractors. But for authors’ purposes, it gives a handy set of conceptual tools we can use. Five major forces that productive cities exert on other cities or regions; four examples of what happens to regions when those forces are out of balance. Easy to wrap your head around, but rich enough to generate lots of story texture.

Plus, material for new stories. (How many fantasy stories spend a lot of time on the trade between cities? I’d sure like some more.)

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(This post is part of Politics for Worldbuilders, an occasional series. Many of the previous posts in this series eventually became grist for my handbook for authors and game designers, Beyond Kings and Princesses: Governments for Worldbuilders. The topic of this post belongs in the planned second book in this series, working title Tyranny for Worldbuilders. No idea when it will be finished, but it should be fun!)