In the short term, this modern version of a 19th century British colonial technique may actually serve to beat back the al-Qaida-related bands, as it reportedly has in Anbar province. But in the medium term, it can only fuel the civil war that most observers expect to erupt with full fury as American and British forces pull back. And that's in addition to arming the largely Shia forces of the Iraqi army. One way or another, Americans are giving Iraqis more weapons with which they can kill each other. After yesterday's attack on the al-Askari mosque in Samara, another round of Sunni-Shia violence must be expected.

The surge is due to be over next April. A new president will be elected in November. What will he or she do about it? Let's start with the she. "What I'm trying to do now," said Hillary Clinton in a discussion broadcast by CNN last week, "is to figure out how we get out of Iraq and how we get out as soon as possible." Well, that's clear enough. John McCain and Rudy Giuliani are talking a very different language: one of resolution, staying the course and winning the fight. But some of their lesser-known Republican competitors have other ideas.

Senator Sam Brownback, for example, proposes partition into three states: Kurdish, Sunni and Shia. Tommy Thompson, a former secretary of health and human services, says each of the 18 territories in Iraq should elect its own leaders, "and if they do so, the Shias will elect Shias, Sunnis will elect Sunnis, Kurds will elect Kurds. And you know something? People will go to those particular territories, and you get rid of this civil war." Get rid of it by ethnic cleansing, that is.

On the ground in Iraq, the bright ideas of distant politicians can be written out in blood. McCain himself sees and warns against this. "You would have to divide bedrooms in Baghdad," he says, "because Sunni and Shia are married to each other." If the United States followed Brownback's proposal, "you [would] withdraw to the borders and watch genocide take place inside Baghdad". But it may yet come to that, even if it is only to the Green Zone that US troops withdraw - and McCain has not convincingly told us how he would prevent it. Already there are hundreds of thousands of Iraqi dead, wounded and bereaved. An estimated 2 million Iraqis have fled the country and another 2 million are internally displaced. It can hardly get worse, we say. Then it does.

I hope very much that I am wrong, but it now seems likely that future historians will see Iraq as an American defeat as big as that in Vietnam, though different in kind. It's not yet, and may never be, a case of the helicopters taking off from the flat roof of the embassy in Baghdad - as happened in Saigon - but it's already something tragic and pitiful. The most powerful military in the history of humankind, with a total budget now in the order of $500bn a year, is reduced to handing out arms to local brigands in a desperate attempt to halt the spread of violence and anarchy. Thereby it piles up more tinder for future violence and anarchy.

President Bush's new coordinator for Iraq and Afghanistan, Lieutenant General Douglas Lute - "pronounced LOOT", a White House handout helpfully explains - says that the two countries "represent what we in the military call the main effort in the long war". This notion of "the long war" is now official doctrine, enshrined in Pentagon reviews and the president's 2006 state of the union address, and quietly supplanting the post-9/11 "war on terror". Yet Lute himself emphasised three main points about Iraq in his confirmation hearing before the US senate: there is no purely military solution; there is no purely American solution; and the solution can be found only in the context of the region. No one knows better than the intelligent soldier the limits of what soldiers can do.

However, the logic of Lute's argument needs to be taken a step further. Rather than "the long war" we should talk about "the long struggle", a term suggested by Bruce Berkowitz in a recent article in the journal Policy Review. The term "struggle" rather than "war" emphasises still more clearly Lute's point that this is not to be won solely or even mainly by military means. As Berkowitz writes: "Military power will be important, but soft power - American culture and international commerce - will, over time, have a greater effect in defeating or transforming our adversaries."

Against whom is this long struggle directed? Mainly against a new wave of international terrorism, often inspired by extreme, jihadist versions of Islam, though also by other grievances; and characterised by the readiness to use suicide bombing and the exploitation of growing possibilities for asymmetric warfare against even the most technologically sophisticated army in the world. Not the least part of the tragedy of the Iraq war and occupation is that it has, in manifold ways, fuelled the flames of international terrorism that it was meant to extinguish. The challenge was there well before Iraq; if one has to give this new wave a starting date, one might go back to the Iranian Islamic revolution of 1979. But Iraq has made it worse. This may not be the biggest challenge the world faces in the early decades of this century - climate change and ensuring that the "peaceful rise" of China remains peaceful are arguably bigger ones - but it is real and nasty enough.

What would be victory in this struggle? Nothing so clear-cut as victory in an old-fashioned, conventional war. It would be more like what happened with earlier waves of terrorism, whether anarchist in the early years of the 20th century, anti-colonial in mid-century, or left-revolutionary in the 1970s. No enemy is defeated on a field of battle, but the diffuse threat is gradually contained and eroded. Britain's official anti-terrorism strategy defines the aim thus: "to reduce the risk from international terrorism, so that people can go about their daily lives freely and with confidence". That cautious, even pedestrian, formulation would not do for the ending of any western, but it's exactly what we need.

One other conclusion follows from this analysis - one even the most intelligent general would be reluctant to spell out. To help win this long struggle, the United States needs to take a whole chunk of that $500bn from the military and spend it in other ways. Now which of the presidential candidates will step forward to propose that?



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