Some 19 US soldiers have been killed so far in December, the lowest number of American military fatalities in a single month since the invasion of Iraq in March 2003. As recently as May this year, 135 US soldiers were shot dead or blown up by Iraqi guerrillas.
The fall in US casualties is one of the most surprising events of 2007. At the beginning of the year, the American army in Iraq seemed to be clinging on by its fingertips as more and more of the country came under the control of Sunni and Shia warlords. Twelve months later, US units are peaceably patrolling districts of Baghdad where once they faced ambushes at every street corner.
Viewed from the White House, events in Iraq seem to be one of the few optimistic developments in the series of crises facing it in the central core of the Islamic world, as the fragility of the US position is underlined by the assassination of Benazir Bhutto, one of its main allies, in Pakistan.
Iraqis and the outside world are equally perplexed as to what this means. Are we seeing the beginning of the end of the fighting in Iraq, a conflict which has now gone on for longer than the First World War? Or is it a lull in the violence that is bound to end because Shia, Sunni, Kurd and American are as divided as ever?
Significant changes have taken place in Iraq this year. The most important is that part of the Sunni Arab community, the core of the insurgency against the US occupation, has changed sides and is now fighting al-Qa'ida in alliance with the US military. This dramatic switch in allegiance occurred primarily because the Sunni Arabs, only 20 per cent of Iraq's population, were being overwhelmed by the Shia, the branch of Islam to which 60 per cent of Iraqis belong.
The US and British armies have examined many past guerrilla wars, looking for parallels which might prove useful in combating the Iraqi insurgency.
British generals were once particularly keen on proudly citing their actions in Malaya and Northern Ireland as providing rich experience in anti-guerrilla warfare. Most analogies were highly misleading. "Basra was the exact opposite of Northern Ireland and Malaya," a British officer told me in exasperation. "In the latter we were supported by the majority communities while we fought the Roman Catholic and Chinese minorities. In southern Iraq our main problem is that we had no real local allies."
The Americans suffer from a similar problem in central Iraq. Outside Kurdistan, it is difficult to find an Iraqi who supports the US occupation for more than tactical reasons. Seldom mentioned, for obvious reasons, is the one recent anti-guerrilla war which has many similarities to that being fought by America in Iraq. This is Russia's successful re-conquest of Chechnya between 1999 and the present.
In a similar way to al-Qa'ida in Iraq, the Islamic fundamentalists in Chechnya, invariably called Wahabi, played an increasingly central role in the armed resistance to the Russian occupation. But the savagery of their fighters alienated many anti-Russian Chechens and eventually split the insurgency. I remember being astonished that Chechen human rights workers, who usually denounced Russian atrocities to me, were prepared to co-operate with the Russian army to attack the Wahabi. Often their motive was a blood feud against a Wahabi commander who had killed their relatives.
The parallels between Iraq and Chechnya should not be carried too far. The US has effectively raised a Sunni militia force which may soon total 100,000 men, many of them former insurgents. They are armed and paid for by the US, but regard the Shia-Kurdish government with deep suspicion. Many Sunni commanders speak of taking on the Shia militia, the Mehdi army, which has been stood down by its leader, Muqtada al-Sadr.
It is a bizarre situation. One experienced Iraqi politician told me that al-Qa'ida in Iraq, which never had much connection with Osama bin Laden's organisation, had effectively split last year. A sign of this was when somebody betrayed the location of its leader, Abu Musab al-Zarqawi, to the US military, which bombed his hideout and killed him. Some of the so-called "Concerned Citizens" militiamen now on the US payroll are former al-Qa'ida fighters, though the US is still holding hundreds of men in Guantanamo, accusing them of being associates of al-Qa'ida.
The US has had real operational successes on the ground in Iraq this year, but there is little sign yet of Iraq being pacified. Local warlords in Sunni areas have switched from attacking US forces to working with them, but they might easily switch back tomorrow. As with the British in Basra, the Americans lack long-term allies that can stand on their own feet without US assistance.
This is one of the dangers of the continuing US presence. The longer it goes on, the more the government of Iraq becomes incapable of existing without US support. The government in the Green Zone is a hothouse plant that would wither and die without the American military presence. Although prime minister Nouri al-Maliki complains about the way in which the US controls the Iraqi army, he makes little practical effort to move out of the Green Zone or establish his practical independence. The US may say that it will leave when the Iraqi government can stand on its own two feet, but the continuing occupation makes sure that day does not come.
Iraq, Afghanistan and Pakistan are very different countries, but they are the terrain in which President Bush chose to test America's status as a superpower. They are also countries where it is difficult to win a decisive victory because power is so fragmented. Successes often turn out to be illusory or exaggerated. For instance, the Taliban was so swiftly overthrown in 2001 because the local warlords, whom the Taliban had bribed or intimidated into supporting it, found that the US offered bigger bribes and its bombers were more intimidating. They changed sides once again, though very few of them went out of business.
The same is true of Iraq today. Iraqi parties, movements and communities have an extraordinary ability to withstand outside pressure. Most of them survived Saddam Hussein and are not going to buckle under anything the US can do to them.