Whenever commentators have run out of inspiration during the long march of festival screenings, there's always that lazy column filler about how politics is taking over the cinema. We've heard it about Cannes and Berlin in recent years, based on the success of overtly political polemical documentaries, notably from Michael Moore. And we're hearing it again now. Such polemics have carved out a following but politics is far more powerful in film as allegory - as McCarthy and his anti-Communist witch hunters were only too aware in the 1940s and 1950s.

Far more interesting is whether the political centre of gravity has changed in the film world in any significant way and, if so, why. Perhaps the last time we had so much interest in politics and film was during the 1980s, with a series of films reappraising the Vietnam war. It may have opened up wounds in the US but for the rest of the world, such films felt like a superpower at the shrink, opening up after a decade of repressed emotions.

It's natural to think of the current crop of Iraq/Afghanistan-based Hollywood films in the same terms. President Bush's recent explicit comparison between the Iraq and Vietnam wars has further spurred interest.

Most US Iraq films follow pretty much the same theme of heroic working-class soldiers fighting what Tommy Lee Jones this week calls a 'fraudulent war' - lions led by donkeys.

But the Vietnam war was rewritten cinematically from a relatively safe distance and the films were still explicitly exploring the US psyche.

Iraq, Afghanistan and terrorists from extreme Islamic groups on the other hand are issues rooted in the here and now for the whole world.

These are matters that resonate across the planet and at least seem to affect everyone (Mao once said it was too early to judge the impact of the French revolution but now everyone wants instant judgement).

So here's the argument: the influence of international markets on film-making is shifting the politics of film - or at least which films are financed and find distribution.

For many on the right it's just a case of film-makers, and particularly Hollywood, pursuing its liberal counter-culture agenda but that's only a half truth.

In the rest of the world, it is more common to see Hollywood as the embodiment of US cultural imperialism. But the motivation for the studios and anyone looking to make films commercially these days is what will sell across international borders.

A little anti-Bush sentiment is not going to harm global box-office one jot. Even those countries that sent troops to help the US have a majority of their populations opposed to the war.

Liberal is not a pejorative term in most countries that studios want to reach and that seems to be reflected in the full range of content.

It's quite possible to find signs of the change in this summer's blockbusters. The baddies have often been evil corporations, the goodies as keen to save Paris and London as the US of A. Remember Superman's dumping last year of the American Way in his 'Truth, Justice...' mission statement'

Bringing down trends to mere economics may seem a little reductive (though Karl Marx would have thoroughly approved) but take a look at the summer. Estimates put US box office (including Canada) at a shade over $4bn but the international market was worth $4.3bn from studio blockbusters alone, before you add in independent and local fare.

None of this is to doubt the sincerity of the film-makers who are grateful to have the opportunity to make a heartfelt statement.

But a liberal shift should probably be seen more in terms of good business right now than some deeper ideological change - the surrender monkeys are buying tickets. To a growing extent history is being written not by the winners but by the market.