If the EU tries to stop its constituent economies going global, I surmise from working trips to Milan and Amsterdam that it is terrible at it. These cities gleam with graphic evidence that Brussels is not the dead hand of Eurosceptic lore. It is either an enabler of mercantile openness or, at worst, an irrelevance.

With all rich regions, the complicated relationship is (or should be) with their own countries. It is the nation state that taxes their output and sends the receipts to other areas. It is the nation state that can act against their interests through sheer weight of electoral numbers. Ask Londoners. Next to this, the EU, for all its supranational pretensions, asks nothing of them.

So why are there not more Catalonias? Or more Venetos and Lombardys, the two Italian regions that voted for more autonomy on Sunday? And might there be in future? Catalans have a stronger ethnic identity than most regional populations but the other raw materials of separatist feeling, which seem to include economic self-reliance and historic experience of self-rule, are there in city-regions across Europe and beyond.

The material gap between cities and deindustrialised heartlands has grown over decades to become the most troublesome faultline in western democracies. Look at an electoral map of votes for Donald Trump in America, Marine Le Pen in France or EU exit in Britain.

But the real trouble starts when we see this imbalance exclusively through the lens of the left-behind places, as something to be redressed through infrastructure projects, industrial protection and a new cultural sensitivity to conservative-minded provinces.

As a moral proposition, this is right: the weakest first. As a reading of how politics will actually unfold over time, it could be the wrong way around.

The anger that poor regions feel for the rampant metropolis – that Pas-de-Calais feels for Paris, that Indiana feels for New York – might turn out to weigh less than the grievances that flow in the opposite direction. In this version of the future, it is the city dwellers who feel wronged by regions that free ride on their productive surplus and vote against their heathen ways from a distance. (Call it representation without taxation.)

National governments find it harder to raise revenue from the one to subsidise the other. Regionalist movements emerge, pressing for greater and greater autonomy if not formal secession.

Assumption of permanence

In the absence of ethnic homogeneity, it is automatic fiscal stabilisers that mark out a nation. Nationhood is the willingness of rich regions to pay for the rest as a matter of course. If that willingness goes away, the nation becomes form without substance.

Might it? If anything characterises the present-day conservative, such as President Trump’s former adviser Steve Bannon or the people who brought you Brexit, it is a habit of talking about the nation state as though it were a non-negotiable constant of history rather than an improvisation of recent centuries.

There is something of the arriviste about them, forever reading heritage into a mock Tudor mansion. The nation is too young to deserve this assumption of permanence. It emerged before the welfare state, when fiscal transfers between regions were too small to constitute a burden on anyone. It also predates a global economy whose returns are to knowledge and capital, which convene on cities rather than to land and industry. It is curiously untested by the modern world.

Some Londoners dream of a sovereign republic, with a moat dug around the M25 and passport checks at Watford, but it is an improbable candidate by European standards. England became a political unit a millennium ago. Even if the UK were to flake away around it, there is still a nation in which London is immemorially enmeshed. Being the capital also serves as compensation for all the wealth sent elsewhere.

It is the continent that is worth watching. Some of the richest European cities governed themselves and their surrounds for longer than the countries they now find themselves in have existed. Most do not have capital status as a sop.

There will be no restoration of the city states, no undoing of the Risorgimento, no secessions in Hamburg and Bordeaux. But there is every prospect of cities demanding more self-rule as relations deteriorate with nations that seem to need and resent them all at once.

If conservatives cherish the nation state, they cannot become a one-sided lobby for the angriest provinces. That is an abusive relationship, not a country. The long-run threat to nationhood comes from productive, outward-facing regions that look at their domestic stragglers and feel – to steal a phrase – shackled to a corpse.

Copyright The Financial Times Limited 2017