Why the Countryside Emptied

In 1800 roughly three people in a hundred lived in a city of more than a hundred thousand. Today more than half the world's population is urban, and the crossing point was somewhere around 2008. That is among the largest and fastest changes in human living arrangements that has ever occurred, and it is easy to miss because it has no event attached: no treaty, no battle, no single year.

The usual explanation is that cities attract people, and that is the second half of the story. The first half is that farms stopped needing them. Mechanisation, selective breeding and above all synthetic fertiliser cut the labour required per field by something close to an order of magnitude. A workforce that had been necessary became surplus, and surplus people have to be somewhere. Framing the movement as attraction alone makes it sound like a preference, which for most of the people making it was not the most accurate description.

Demographers separate this as push and pull, and the balance between them turns out to decide what kind of city you get. Where industry is pulling (Manchester in 1850, Shanghai in 1990) the city grows because there are jobs, wages rise, and eventually the wages fund the sewers, the building codes and the housing. Where push dominates and industry does not follow, a city can reach ten million people on informal work alone, and the mechanism that historically converted urban misery into urban improvement is simply absent.

That is why twentieth-century urbanisation in much of the world looks superficially like the industrial city and works nothing like it. The density is comparable. The income is not. Manchester was appalling and it was paying, and the paying is what eventually made it liveable.

A second distortion is the primate city: one city far larger than the next in its country. It is usually an inheritance. Ports built to export to a metropole, capitals holding every ministry and every university, rail networks built to reach a single point rather than to connect a country: each concentrates everything in one place, and the result is a national economy with one node. It is fragile, it drains the regions of anybody ambitious, and it is much easier to create than to undo. Several countries have spent decades and entire purpose-built capitals trying.

Then there is the informal settlement, which houses something like a billion people. It is housing built outside the legal system because the legal system cannot supply it fast enough, on land whose ownership is unclear, and it is the direct modern equivalent of the back-to-back: the cheapest thing that can be built at the incomes available. Treating it as an aberration leads to clearance, which the twentieth century attempted repeatedly and at scale. Treating it as housing that needs water, drainage and secure title has a considerably better record.

Which leaves the policy that keeps being tried and keeps failing: restricting movement into the city. Residence permits, internal passports and outright bans have all been used, and the consistent result is a large population living in the city without legal status rather than a smaller population living outside it. The people released by agricultural change have to be somewhere, and the countryside no longer has work for them. The interventions that have actually made a difference are the ones that put work somewhere else, which is slow, expensive and unglamorous.