The elite are in trouble, their sources of wealth exhausted, their civilisation assailed by crazed fanatics from without – while, within, the masses are in open revolt. No, it’s not the eurozone – it is Westeros, the mythical venue for Game of Thrones.

It was JRR Tolkien, the father of fantasy fiction, who summed up the attraction of a genre that has become, in the past 60 years, a staple of modern culture: “a Secondary World into which both the designer and spectator can enter, to the satisfaction of their senses while they are inside”.

But why do so many of these secondary worlds resemble feudalism in crisis? From Tolkien and CS Lewis, through to interstellar worldbuilders like Frank Herbert in Dune, and now Game of Thrones itself, the most successful fantasy worlds invoke not just the trappings of feudalism – kings, torture and trial by combat – but the actual crisis of feudalism.

In modern fantasy fiction there is always a crisis of the system: both of the economic order and of the auras of power – the magic– that emanate from it. There is, in literary theory, even a technical term for this critical point:“thinning”. In their Encyclopaedia of Fantasy, John Clute and John Grant define thinning as “the constant threat of decline”, accompanied by a pervasive mourning and sense of wrongness in the world.

As Westeros girds its gym-toned and wax-depilated loins for season five, the thinning process is well under way. There is the encroachment of the spirit world from the icy north; there is a slave revolt happening across the sea.

But there is also more clearly systemic doom hanging over the economy of Westeros. The ruling Lannister family obtained its wealth from owning most of the gold mines. The currency of Westeros is tri-metallic: there are gold, silver and copper coins deriving their value from the metal contained in them – not from a central bank and its “promise to pay” as in real life.

The problem is, in season four, the Lannisters’ big cheese, Tywin, dropped a bombshell: the gold mines have not produced for three years. On top of that, the Lannisters owe loads of money to something called the Iron Bank. “All of us live in its shadow,” says Tywin, “but none of us know it. You can’t run from them, you can’t cheat them and you can’t sway them with excuses. If you owe them money, and you don’t want to crumble, you pay it back.”

If this sounds a lot like Greece and the European Central Bank, that’s only because their current standoff replicates the essential power shift that happened towards the end of feudalism: debts accumulated under a corrupt patronage system, whose sources of wealth dried up, destroyed the system in the end.

If you apply historical materialism to Westeros, the plot of season five and six becomes possible to predict. What happened with feudalism, when kings found themselves in hock to bankers, is that – at first – they tried to sort it out with naked power. The real-life Edward III had his Italian bankers locked up in the Tower of London until they waived his debts.

But eventually the power of commerce began to squash the power of kings. Feudalism gave way to a capitalism based on merchants, bankers, colonial plunder and the slave trade. Paper money emerged, as did a complex banking system for assuaging problems like your gold mine running dry.

But for this to happen you need the rule of law. You need the power of kings to become subject to constitutional right, and a moral code imposed on business, trade and family life. But that won’t happen in Westeros, where the elite lifestyle is synonymous with rape, pillage, arbitrary killing, torture and recreational sex.

So what Westeros needs is not an invasion of werewolves from the frozen north, but the arrival of a new kind of human being: they should be dressed in black, with white lace collars, stern faces and an aversion to sex and drink. In a word, Westeros needs capitalists – such as those who frown puritanically at us from Dutch portraits in the 17th century. And they should, as in the Dutch Republic and the English civil war, launch a revolution.

But that can’t happen in the secondary world of fantasy fiction. The thinning process can never be allowed to end; it must be perpetual for the conceit of the drama to work.

There is a reason so much fantasy fiction adopts the conceit of a feudalism that is always in crisis but never overthrown. It forms the ideal landscape in which to dramatise the secret desires of people who live under modern capitalism.

Tolkien’s generation – scarred by industrial-scale warfare – craved the values of heroism and mercy associated with the face-to-face combat of yesteryear. For William Morris, whose utopian socialist novel News From Nowhere is set in a quasi-medieval Hammersmith, the craving was for skill, craft, beautiful individual objects – an escape from the brutalism of industrial mass production.

Future social historians, as they look back on the popularity of Game of Thrones, will not have much trouble deciphering the inner desires of the generation addicted to it. They are: “all of the above” plus multipartner sex.

Trapped in a system based on economic rationality, we all want the power to be something bigger than our credit card limit, or our job function. Nobody sits at home watching the these dramas imagining they are a mere slave, peasant or serving girl: we are invited to fantasise that we are one of the characters with agency – Daenerys Targaryen, a beautiful woman with tame dragons, or the unkillable stubbly hunk that is Jon Snow.

It is for social psychology to explain the enduring popularity of fantasy, and its evolution towards soft-porn gore. All political economy can do is point out the contraditions and where they lead.

So sometime in season five or six, I predict the Lannisters are going to fall, as the feudalists did, unless they discover some previously unknown territory, full of gold and easily killable people, just as the Spanish monarchy did during the real-world crisis of feudalism.

It has always been a mystery as to whether there is a land to the west, across the sea from Westeros. My suspicion is: there has to be, and someone will soon be despatched to find it.