You might have thought that a film called The Karate Kid would be about a young person (or goat) who practises karate. Such was indeed the burden of the 1984 film bearing that title. In the current remake, however, it's kung fu that saves the junior hero's bacon. This martial arts metamorphosis reflects more than a change of cinematic fashion.

Over the decades, Hollywood's geopolitics have tracked those of its host country. In the 1980s, Japan and its dark arts were a matter of national concern: the Japanese were presenting an unexpected challenge to American economic pre-eminence. Somehow, they were not only out-competing American industries but actually gaining control of them. In 1989, Sony even bought Columbia Pictures.

On screen, karate became something of a metaphor for Japan's mysterious but devastating capabilities, enthralling audiences in films ranging from Showdown in Little Tokyo to the original Karate Kid. However, in the 1990s, Japan collapsed into its lost decade of recession, and so did much of the threat it had seemed to pose. Thereafter, the movies lost their passion for karate.

Now, however, China presents the US with a greater challenge than Japan ever did. The People's Republic has somehow acquired a stranglehold over America's finances; worse, it threatens to displace the country as the world's leading power. Americans are well aware of this and feel not only anxious but intimidated. Once more, it seems, a martial art is standing in on screen for the unfathomable powers of an inscrutable national adversary.

Like the earlier film, the current Karate Kid shows an American youngster appropriating his enemies' techniques and turning them against their malevolent practitioners. Things have, however, deteriorated since 1984. Then, matters could be happily resolved within the comforting embrace of sunny California. Then, the eponymous hero's oriental mentor was a grateful transpacific immigrant who'd fought for America against the land of his fathers.

This time, however, it's Americans who're the importunate immigrants. Jaden Smith's Dre Parker and his mom are fleeing Detroit, the city that's become a byword for America's economic distress, to seek a better life in thriving China. The sunny setting for decisive events has become Beijing, a glittering metropolis peopled by happy, healthy and sporty citizens who're treated as deferentially as their capital.

Unlike his 1984 counterpart, Jackie Chan's kung fu master is an uncompromised product of his country. Mr Han commands not just the exacting physical skills on which success depends, but also mental moxie. He's reluctant to pass on these assets to a self-indulgent young round-eye who's too lazy to hang up his jacket, but pity leads him to relent. Unfortunately, this is a quality much lacking among his compatriots.

Beijing's playground bullies are kung fu fanatics who're all too ready to lay into an American wimp. Their motto is: "No weakness! No pain! No mercy!" Unless young Dre can learn their methods, he'll stand no chance against them. Thanks to Han's selfless guidance, he's able to get initiated. Even so, it's clear that he'll still be at a disadvantage compared to his inevitably more practised opponents.

What saves Dre is that he turns out to have something they don't. They may be trained, disciplined and ruthless. He, however, has humanity. Like any self-centred American adolescent, but unlike the robotic Chinese, Dre's in touch with his feelings. Understandably in the circumstances obtaining, he's frightened. Somehow, this fear enables him to prevail over his enemies.

Superficially, the moral appears to be this. Americans may have allowed themselves to become feckless, idle and otherwise pretty useless in comparison with their eastern challengers. Nonetheless, the regard for their own emotions in which they luxuriate may prove an unexpectedly effective weapon against their otherwise invincible rivals.

So on the face of it, The Karate Kid offers reassurance. Unfortunately, this is unlikely to buoy up audiences beyond the closing credits. Even Americans will find it hard to convince themselves that their niceness will defeat an implacable foe. Smith succeeds in making Dre seem cute; he never makes him look like a genuine winner. The film's actual message is therefore one of foreboding. This time, America, it really seems to be saying, perhaps the game is up.