When Times correspondent George Steer entered the city of Guernica in April 1937, what struck him were the incongruities. He noted precisely the bombing tactics “which may be of interest to students of the new military science”. But his report begins with a long paragraph describing the city’s ceremonial oak tree and its role in the Spanish feudal system.

Sitting in Athens this week, I began to understand how Steer felt. Sunday’s referendum will take place under a kind of financial warfare not seen in the history of modern states. The Greek government was forced to close its banks after the European Central Bank, whose job is technically to keep them open, refused to do so. The never-taxed and never-registered broadcasters of Greece did the rest, spreading panic, and intensifying it where it had already taken hold.

When the prime minister made an urgent statement live on the state broadcaster, some rival, private news channels refused to cut to the live feed. Greek credit cards ceased to work abroad. Some airlines cancelled all ticketing arrangements with the country. Some employers laid off their staff. One told them they would be paid only if they turned up at an anti-government demonstration. Martin Schulz, the socialist president of the European parliament, called for the far-left government to be replaced by technocrats. And the Council of Europe declared the referendum undemocratic.

With ATM cash limited to €60 a day, one shopkeeper described the effect on her customers: on day one, panic buying; day two, less buying; day three, terror; day four, frozen. The words you find yourself using in reports, after looking into the eyes of pensioners and young mothers, make the parallel with conflict entirely justified: terror, fear, flight, panic, uncertainty, sleeplessness, anxiety, disorientation.

If the effect was to terrorise the population, it has only half worked. The pollsters are simply finding what Greek political scientists already know: society is divided, deeply and psychologically, between left and right.

The anthropologist David Graeber points out, in his history of debt and debt forgiveness Debt: The First 5,000 Years, that the transaction carries the implicit threat of violence. Debt gives you the power of rightful coercion with all the blame attaching to the victim. But rarely has that power been used as Europe used it against Greece last week. In the 2013 Cypriot crisis, where the EU enforced the seizure of money in people’s bank accounts, the government caved in at the first confrontation.

Greece is different. If I were to pick out the equivalent of Guernica’s symbolic oak tree here, it would be the graffiti. “We didn’t die for love so why would we die of starvation?” reads one plaintive message. Throughout the five years of the crisis, Greeks have been using the walls for mutual public psychotherapy. “I’m being tortured,” reads a popular tag by a famous graffiti sprayer. “I’m spinning,” reads a parody tag that rhymes with it, often found close by, reportedly sprayed by the first guy’s jilted girlfriend.

I’ve often wondered what it would take for the walls to go white again. But there is no obvious answer. The graffiti, like the sporadic rioting and casual ultra-leftism among the young, broke out in 2008 during the two weeks of violence after the killing of 15-year-old Alexis Grigoropoulos by police. That was the modern Greek 1968, and if you measure it against the original, by now, we should be in the mid-70s, a moment of demobilisation and defeat. But whatever the outcome of Sunday’s vote, it is hard to see this mass psychology of revolt and refusal going away. Like the oak tree at Guernica, it can survive financial carpet-bombing.

What worries me now is whether Europe can survive the act of inflicting it. Sitting in their ministries, the Greek negotiators were coolly drawing parallels with the 2005 Dutch and French referendums on Europe, where no votes led to a change in the European offer and a yes thereafter. But they had misunderstood. To drive a country to the point where its banks close and its pharmacies run out of medicine is not done to force a mind change. The aim was, as Telegraph journalist Ambrose Evans Pritchard wrote, regime change.

But here lies the central problem. Most of the time, when states deploy decisive measures against other states they have a plan not just for who will govern but what the replacement system will be.

Germany’s mistake, in this sense, since 2010, has been its failure to demand a modernised and productive capitalism. It imposed European debt rules via parties who were never prepared to impose the European norms of business and social equity. Indeed, the EU has relied on a local business elite that is often physically absent: happier in Knightsbridge than in its Athenian equivalent.

When Angela Merkel and Nicolas Sarkozy overthrew first George Papandreou and then Silvio Berlusconi, they could at least console themselves that it was a political mercy killing. Not many people rioted. And as Sarkozy implied, when he slapped me down at a press conference, this was the European way.

After this week, the narrative of the EU as “imperialist” will blossom in Greece – but true imperialisms imposed order. The outcome here is likely to be very different.