Wired on Friday: This American presidential election promises to be one of the most tense and scrutinised in history, both inside and outside the United States. Much of the scrutiny, analysis and pure partisan screaming is found on the internet - far more than any previous election. But what effect is this having on the electorate, or for that matter, the world?

One of the miracles of the US is that it has maintained two centuries of democratic traditions while at heart being a country of stark extremes.

From the radicalism of its founding principles, to the precipitous distances between rich and poor, to its histories of assassination and social agitation, to some of the most disturbing racism and repression, it has somehow contained it all within one national border and one political process. The southerner and the northerner, with the barest minimum of shared values, somehow see themselves as both American, and have worked together to build their country.

In part, the United States has handled this schizophrenia of national personality by being both large and mobile. In America, if you don't feel comfortable where you live - and you can afford it - you move to where they like what you have to say.

In the political arena, diverse groups have always met and clashed in America at the national level, but always with the slow, measured pace of election cycles and legislative sessions. Distance and time: those filters have a moderating effect.

But now, thanks to the net, the factions of American thought have a direct line to each other. Whether it's the southern character, spoken proudly by many of the conservative writers on the net, or the New England and California progressive liberals, all voices are heard - and instantaneously. Everyone is a neighbour.

That's not always a good thing. How many of us like the neighbours we already have? The dialogue between all these sides has become fast and hard, no longer tempered or filtered by the media. Left and right voices, untempered online, often reduce themselves to the absurd quickly, whether it is exclaiming that Bush is exactly like Hitler, or late night essays extolling a policy of cultural extermination against all Islamic Arabs.

Neither of these positions represents much more of a fraction of the population than they once did, but both have a far greater readership than they ever could have enjoyed in the past - both from people who find themselves troubled to have these people supposedly on their side, and by people that use these voices as justification to write off more reasoned opponents altogether.

The fast dialogue between right and left has taken its toll, and left less and less middle ground. But neither extreme is a disenfranchised minority. With their new voice, they also find a modicum of power. The net has created a sense of participation and mobilisation like never before - with groups like Moveon.org using the Net to solicit and run adverts, create calling networks, voter outreach programmmes, and so on. Amateur commentators writing on their online blogs have contributed to the resignation of a high ranking Republican after a racist comment made at a birthday party, and exposed the memos published by CBS as obvious fakes within hours of their release.

That the right battles the left in America - and the whole world is watching - is a story we've lived with for some years. We haven't needed the net to tell us that. But now we can watch the American left's grassroots talk first hand, with sites like www.democraticundergound.com and atrios.blogspot.com; and we can hear America's right, too, with sites like www.instapundit.com and www.rightwingnews.com. The fight has become too close for comfort.

And, perhaps most disturbing, they can hear us talking about them, and lean out of the news to talk back - as the Guardian recently found out.

After initiating a programme to target a swing county in Ohio with international letters through downloads of addresses off the internet, the Guardian itself was targeted by conservative bloggers crying foul for the perception of international interference in a national election.

The response was an email campaign of anger, complaint, and even death threats aimed at the newspaper's staff. The Guardian ended their campaign earlier than they wanted to, but still called it a success after reaching 14,000 letters written. The bloggers also crowed about their success, and haven't let up on the Guardian.

Last week, Charlie Brooker, one of the Guardian's TV reviewers, made an offhand comment about Bush and Lee Harvey Oswald. It's the sort of joke most Guardian readers would dismiss with a mild smile. But outraged Americans attacked the site again, causing the Guardian to withdraw the article with an apology. A British newspaper, previously content to act as an observer to the American story, had been made an uncomfortably close participant within it.

Within America, all this activism and scrutiny isn't likely to end on November 2nd, whichever man is elected in this tight race. Left and right are already filing court cases, with websites dedicated to following and disseminating their progress. Voices on both extremes have already rejected any outcome that doesn't match their desires.

They'll be filling the web with revelations of tampering with the American election system (something which history shows is something of an American tradition in itself) but has come to light in new ways on the net.

Hundreds of thousands of Americans are reading and already planning to keep fighting on long after November - a result that threatens to polarise American discourse even further.

And as the internet spreads around the world and more and more obscure voices become a Google search away, that polarisation promises to go far past the American border.

Whether it's political freedom in China, or immigration issues in Europe, or corruption in Africa, we are likely to be seeing more of the sides to our neighbors than we've seen before, and more complicated pictures of our friends and enemies.

And our own actions, previously comfortably buried in our own media and society's conformity, will be exposed to the rest of the world. The crudest brickbats thrown at the Guardian's readers by its American critics were about the bad teeth of the British. The most pointed were about Britain's own history of intervention in other country's affairs.

Well, like it or not, we all have our national bad teeth - controversies so burnt into our national psyche that we barely mention them in our own media for fear of shaming us all, or laying bare our own divisions. Thanks to the net, we'll all soon have an international audience to point these things out.