The danger of this growing fashion for nostalgia

Human beings used to have, Tom Cruise implies, a spiritual and ethical balance that has been lost

Ah, the wisdom of the Samurai. Tom Cruise is merely the latest recruit to that fearless band of Central Park Samurai, millionaire Americans who have turned for spiritual guidance to the overlords who ruled feudal Japan from the eighth century until the early 19th.

Jim Jarmusch, the indie director who's so cool he's frozen, began the American fetish for this culture a few years ago with his movie Ghostdog: Way of the Samurai. It's the everyday story of a New York hitman who lives by the ancient Samurai code. Soon after the film's success, Samurai textbooks became best-sellers, and now Mr Top Gun himself is slashing his way to a multiplex near you.

If the film were just another Hollywood brain-buster, I wouldn't trouble you with the details. But Tom Cruise has captured on celluloid - absurd though it may sound - a feeling that is resurgent in the West. He has taken an intense hatred of modern life, married it to nostalgia for feudalism, and crafted it into three hours of cinema. The film is terrible, but it matters. It matters because it expresses a suspicion that many people feel but leave unspoken.

The suspicion is simple: modern life is a failure. When, two centuries ago, our predecessors abandoned subsistence farming for industrial towns, they made a terrible mistake.

If you had the opportunity, wouldn't you warn them to stay as they were? Wouldn't you implore them to burn their factories and return to the land while they still could?

The Last Samurai encourages its audience to think all this. It is the story of Japan's transition from a feudal economy, based on the rule of warlords, to an industrial modern state. It is a eulogy for the simple society of Samurai, which was based on "a life of service, discipline, compassion" and "what seems to have become a forgotten word - honour". Human beings had, Cruise implies, a spiritual and ethical balance under feudalism that has been lost. The transition to modernity - even though it ended with Japan as one of the most prosperous nations in the world - was a tragedy.

These are extremely potent ideas. We cannot ignore them. Books and movies expressing them are flourishing - look, for example, at the amazing popularity of pre-modern Eastern spiritualism in the West. But, more importantly, there are at least two vast global movements today that explicitly pine for the pre-modern world to be restored: Islamic fundamentalism and the "deep ecology" wing of the environmentalist movement, embodied by groups like Earth First!

Islamic fundamentalists see modernity as an evil force corrupting the simple rural values preached by the Prophet Mohammed. Deep ecologists believe that modernity is responsible for an "ecocide", which has decimated most natural life just to clear the way for an ever-growing human population. Modernity, if it is not arrested, will wreck the planet. Only a massive retreat to a simpler form of life, like the Samurai, can save us.

Even if you are not attracted to these twin philosophies, you might still find regression appealing. With the death of pre-modern societies like the Samurai, the Inuit, and the native American tribes, humanity leaves behind the village, the local, the rural, and the slow. We enter a world of densely-packed cities, of confusion, congestion and concrete.

If modernity is not defended, these movements will become increasingly powerful. And the consequences will be catastrophic. We know about the resurgence of Islamic fundamentalism. As environmental disasters proliferate because of global warming, the other great anti-modern hatred - deep ecologism - will also swell.

A global assault on the institutions of modernity - and especially the core modern institution, the city - is brewing. It is time we equipped ourselves with arguments in its defence. First, the illusions about pre-modern societies must be crushed. Like most feudal nostalgists, Tom Cruise does not allude to the fact that the Samurai culture he is rhapsodising about was one of the most patriarchal and misogynistic in human history. There is one woman in the film - one! - and her role consists entirely of lusting for Cruise's body and cleaning his house. Feudal societies are built upon rigid, unchanging hierarchies, and women are always at its base.

Anybody pining for the days of Pocahontas, Excalibur and the Samurai should remember this: in pre-modern societies, power is scattered between disparate groups, which are invariably controlled by violent men. Nothing progressive can form in this environment. Just look at contemporary Afghanistan, where women are the strongest supporters of moving from feudalism to a unified state.

If we seek to shatter the modern world, because of its (often real) sins, this is what we will regress to: a world of male supremacy, and all it entails. (This is why Islamic fundamentalists find it so appealing).

Deep ecologists - who now include Professor John Gray, Charles Windsor and many of the Poujadist French farmers following Jose Bove - need to understand that you can't have the pre-modernity they long for without a pre-modern political system.

We must not be afraid to defend the greatest of all modern achievements: the contemporary metropolis - the sprawling, complex city. This is the pinnacle of human existence. Only in the metropolis can human culture and knowledge reach its bizarre, sublime peaks; only there can 10,000 strangers come together in a city square to hear music. Only in the metropolis can gays, Jews, women, dissidents, democrats and oddballs feel safe. If any form of human life has a mystical quality, it is not the rural village, but the beautiful, insane city.

Yes, cities create pollution and, if unchanged, they endanger the future of the planet. (It may take an environmental catastrophe in the US - a climate change-9/11 - to make its government see this). But the desperately-needed solution lies in technological innovation, not in attacking the modern system that creates that technology in the first place.

The really interesting - and essential - environmental thought is happening not with the anti-modern radical ecologist school, but in the "Promethean" wing of the environmental movement, which is looking for technological answers to climate change. They have come up with solutions that do not involve smashing the modern world we have built. One proposal - discussed at a high-level environmental conference last week - is to seed the oceans with iron. This would encourage the growth of marine micro-organisms that take carbon dioxide from the atmosphere. Pilot schemes have shown this could work - but a backlash against modernity would drain the political will to achieve this.

Like the old song, I see a bad moon rising. I fear the rise of 21st- century populist movements, especially in the developing world, where the effects of climate change will be felt most severely. They will demonise the cities, with their modernity, their "moral depravity" and, crucially, their pollution. They will say the city and the modern are responsible for the horrors to come. They will look, as Tom Cruise has, to pre-modern ancestors for a model of how to live.

Historians will one day see the strange little blip of Western reverence for feudal Japan at the start of the 21st century as another tiny warning signal of a looming backlash against the modern world.

j.hari@independent.co.uk