By Jonathan Marcus BBC defence correspondent

The Taleban regime may be largely defeated but the global struggle against al-Qaeda is set to continue.

Military force will be only one of the tools at the Bush administration's disposal and by no means necessarily the most important one. Legal, diplomatic, and financial measures will all play their part.

This is going to be a battle waged by intelligence officials - policemen and immigration officers as much as by soldiers, sailors and pilots. But the military will have its part to play.

The Predator spy plane has played an extraordinary role

And the peculiar features of the Afghan campaign - a war waged, at least from the American perspective, essentially by air power and special forces - does have some critical lessons that may be applicable to future struggles.

A lot has been said about the primacy of air power. Precision-guided weapons have been used on an even larger scale than before.

Carrier-borne aircraft have conducted the brunt of the sorties, given the relative absence of suitable land bases in the region for tactical strike aircraft.

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Heavy bombers like the B-1 and the B-52 have also played a critical role, dropping the overwhelming bulk of the ordnance expended.

In some cases these giant aircraft have effectively been used for close-air-support missions, something their designers never intended. But a key element of the air campaign was the availability of special forces units on the ground to help to identify and designate targets.

The ground war was largely fought by America's local allies

Of equal importance has been the extraordinary role of unmanned aerial vehicles or UAVs like the Predator and the Global Hawk - the latter with its wide-angle of vision - used for the first time in combat.

Critical advances in computer networking and broadband satellite communications enabled intelligence from the UAVs and other sources - like the radars on board the JSTARS aircraft - to be combined with signals intelligence and satellite images.

This capacity to process information in real time has a long way to go but it is the great novelty of this campaign.

Air power

Reducing the time between "the sensor" seeing a target and "the shooter" being able to engage it is of central importance.

The first combat use by the CIA of armed Predators able to deliver Hellfire missiles against ground targets is another novel feature that is helping to reduce the duration of this "sensor to shooter" process.

Air power advocates have much to ponder.

The relatively minor role of land-based tactical strike aircraft like F-16s and F-15s may influence US force planning in the future. US Navy aircraft performed well but at a massive cost in terms of supporting flights.

Huge numbers of tanker sorties were needed to get these aircraft to and from their targets.

But this was far from being an air war alone.

Special forces were deployed to call in air strikes

There was a ground war but it was largely fought by America's local allies. So to start ruling out significant deployments of US ground troops in any future conflict is premature.

The units that have been used are those designed to move swiftly - soldiers from the Mountain Division - and elements of the US Marine Corps who bring their striking power with them, packed and ready to deploy.

There is a great deal of talk about making US forces lighter and more agile.

Afghanistan confirms this view but technical means have to be found to give such light forces a much harder punch. Little is known about the US and British special forces operations, though here too, I am sure, there will be lessons.

This has been a fairly small-scale conflict involving limited deployments.

But it heralds the dramatic changes that are taking place on the battlefield due to the information revolution - changes that in many ways are still only just beginning.