Afghan insurgents have imported tactics from Iraq
Afghanistan is not Iraq. It should not be necessary to make the point, of course.
But after the overthrow of Saddam Hussein there is a growing resistance in the West to further adventures.
In the minds of many people in Europe, sending more troops to Afghanistan is both dangerous and imperialistic.
It does not necessarily have to be either.
The motives that have led Britain, Canada, France, Germany and other countries to send their soldiers to Afghanistan are very different from those which led the United States and Britain to invade Iraq three years ago.
And the response by most Afghans to the presence of foreign troops in their country is nothing like the hatred and anger which so many Iraqis feel towards the Americans and British.
In Afghanistan, the self-interest of Western countries happens to coincide with that of the Afghan people. We need a peaceful, prosperous and well-governed Afghanistan.
When it is none of these things, it can do us immense damage. The attacks of 11 September 2001 in the United States were planned and organised in Taleban-ruled Afghanistan.
Afghans were ignored by the West after the Cold War ended
The great majority of the heroin that reaches the streets of Western cities comes from the wilder parts of Afghanistan.
Help the Afghan government grow strong, support the living standards of the Afghan people, and we ourselves will be safer.
The trouble is, the West has never seen Afghanistan as a real country. It has always seen it, instead, as a square on the international chess-board.
The overthrow of the Taleban was a triumph of minimalism
In the 1980s, when Ronald Reagan was president of the United States and Margaret Thatcher was the British prime minister, we heard a great deal about the sufferings of the Afghans under the Soviet yoke.
But when the Russians withdrew from Afghanistan in February 1989, the Americans, the British and everyone else lost all interest in the country.
Now it was just an extremely poor country with no natural resources.
In the 1990s, ignored by the outside world, Afghanistan descended into a spiral of insane violence which ended only with the arrival in power of the most perverse and retrograde government in modern times: the Taleban.
The overthrow of the Taleban in November 2001 was a triumph of minimalism. A small number of US special forces and a certain amount of bombing helped the anti-Taleban Northern Alliance to chase them out of Kabul.
The Taleban had been loathed by most Afghans, and their departure was greeted like a new dawn. Britain and America promised they would not lose interest in Afghanistan again.
Then came the invasion of Iraq. All the attention was redirected there. As the resistance movement blossomed and spread in Iraq, its influence spread back into Afghanistan.
The Taleban, which had seemed to be finished, began to grow in influence again. It imported the tactics of the Iraqi insurgents and became a training-ground for Islamic militants again.
Anyone who knows Afghanistan knows how ordinary people there long for peace and prosperity.
The author and commentator Ahmed Rashid writes: "Western forces are still welcome - as long as they are really useful and are willing to both fight and help in reconstruction."
Even the south-east, where the Taleban always had greater support, and where British troops are now going to be based, is less dangerous than Iraq.
They can do a great deal more good in Afghanistan - especially if they learn from their Iraqi mistakes.
British troops can restore their reputation in Afghanistan
The key is to act as partners in Afghanistan, not as occupiers.
One of the most thoughtful American commentators on Afghanistan, Vanni Cappelli, argues cogently that the Western forces need to work with the tribes along the wild borderlands between Afghanistan and Pakistan, where Osama Bin Laden and the Taleban leaders are being sheltered.
Last month the CIA launched a missile attack across the border, killing 18 civilians.
This kind of action against the tribes will not, Cappelli argues, "sway this warrior people if it feels it can uphold its honour and dignity by supporting Islamic extremists. The trick is proving to them that there are better ways to secure these things."
Cappelli is entirely right. If the trick can be performed, Afghanistan will be a safer, better, more prosperous country.
The trouble is, public opinion in the United States still favours the use of force rather than reason.
Although he is a well-regarded authority, Cappelli's eminently sensible article was rejected by 24 American newspapers before finding a home in US Italia.
There is a brief opportunity for a new start in Afghanistan. The Americans could rethink their whole approach; the British could restore their reputation, so battered in Iraq, and other Nato countries could show they can be something more than merely critics on the sidelines.
Let us hope they get it right for a change.