Iraq was the classic campaign which demonstrated the overwhelmingly one-dimensional might of the US war machine on a conventional battlefield and its complete inability to deal with the nationwide insurgency which followed.

Iraq was the classic campaign which demonstrated the overwhelmingly one-dimensional might of the US war machine on a conventional battlefield and its complete inability to deal with the nationwide insurgency which followed.

The Americans lost only 176 men in the three-week blitzkrieg that toppled Saddam Hussein - and 4000 to bombs, booby-traps and snipers in the low-intensity guerrilla struggle of the next five years. Britain's death-toll rose from a modest 37 during the invasion to its current 176.

As Iraq's new democratic government states its intent to have all foreign troops leave its soil by the end of 2011, there are 144,000 US and 4000 British soldiers tied down in pointless garrison duty when they are desperately needed in Afghanistan to tackle the real and growing danger of a resurgent Taliban.

When the euphoria died down in a Baghdad freed abruptly from Ba'ath party dictatorship in May, 2003, Iraqis found themselves living in an occupied state where lawlessness swiftly became the norm and the "liberators" failed to kick-start the crumbling economy at any meaningful level.

The biggest US policy error, taken against British advice, was to disband Saddam's army, unleashing 400,000 armed, trained and penniless ex-soldiers into a fractured society that was beginning to turn to militias for protection and some ethnic security.

The US-led coalition did not have enough "boots on the ground" to impose law and order, far less halt the sectarian killings which the power vacuum spawned within weeks.

America had gone to war relying on shock-and-awe and vastly superior technology for a rapid military victory. What it lacked was any coherent blueprint for the aftermath. It also lacked any understanding of Iraq's three-way antagonisms between Sunni, Shia and Kurd or the complex tribal structure and religious loyalties governing most people's lives.

In the south, the British, at first welcomed on the streets of Basra and able to mount hearts-and-minds patrols wearing nothing more threatening than Tam O'Shanters, quickly became the focus of discontent and easy targets. More important, they lacked the fiscal and physical resources to regenerate a city that had been allowed to decay under Saddam as a punishment for political and religious defiance.

To their credit, history and experience at least allowed the UK's representatives to grasp some of the nuances of the disaster gathering momentum. Even if they had had the military muscle to tackle the Shia gangsters and militiamen head-on, Whitehall had no stomach for the casualties that would have entailed and even less for spiralling peacekeeping costs.

Sensing weakness, Iraq's Mehdi Army launched three distinct uprisings as it jockeyed for political leverage, using unemployed soldiers and poor and embittered Shia youth to attack overstretched coalition forces from Baghdad to Al Amara and Basra.

Extremists from Arabia and North Africa also seized the moment to launch an insurgency under the banner of al Qaeda, forcing the US to liberate cities such as Fallujah, fighting building by building against fanatics only too willing to die for their cause.

Despite some counter-insurgency success and the establishment of a fractious and slow-moving elected government, the coalition has never had complete control of Iraq.

Parts of Baghdad are still no-go areas to US troops. The British, forced by lack of numbers to make deals with militias and losing lives needlessly in resupply runs for outposts in Basra, have withdrawn to a fortified base outside the city.

The UK is unlikely to stay until 2011 beyond a few hundred trainers for the Iraqi government forces. Their only useful function now is as bunker-bound sentries on the main US supply route from Kuwait.