This weekend an army of 11,000 troops, including Britons, is roaming the mountains of southern Afghanistan trying to kill or capture the Taliban. Their professed aim is “to establish conditions” in which government institutions and NGOs can “begin the real work that needs to be done”. Operation Mountain Thrust is the last American venture in the country before Nato takes over next month under British leadership.

The operation, coming after four such failed endeavours, is a show not of force but of face. When the troops return to the security of Kabul they will leave behind a few hundred corpses, some destroyed villages, a thousand new Taliban recruits and tens of thousands of angered and disillusioned Afghans. There is nothing new under the Afghan sun.

The British deployment to Helmand, in southern Afghanistan, makes no sense and visiting Kabul has only made me sure of it. This is quite different from Iraq, where the British Army is embarked on a delicate exercise of extraction.

Helmand is an exercise of insertion and has already cost a British life. About £1 billion is being spent on a base in the desert. Nobody in London or Kabul can offer a clear mission statement for the 3,300 soldiers garrisoning it, only implausible remarks about “establishing the preconditions for nation building”.

David Richards, the ebullient British general in Kabul, puts the best possible face on things. To emphasise the newness of his strategy he derides the Pentagon’s four-year-old Operation Enduring Freedom as counter-productive and stresses the anarchy into which it has allowed Afghanistan to fall: 80% of the country is no longer under the control of Kabul.

At least American policy had clarity. As Michael Gordon and Bernard Trainor make plain in Cobra II, their recent study of the war on terror, to Washington Afghanistan was never like Iraq. It was not about neocon nation building but was a hunt to find Osama Bin Laden, “albeit with the wrong search party”. Once a puppet ruler had been found in Hamid Karzai, America was happy to dump the job of propping him up on Britain and others. It even abandoned poppy eradication as a reward to the drug lords for their (temporary) support. The policy was cynical but it was a policy: punch hard and get out.

Richards is a victim of Britain’s post-imperial romanticism. He must go back in. His plan is for “Malayan inkspots” across the country, holding isolated villages long enough for local leaders to win support against insurgents. There will be no more American-style bombing of villages and wedding parties. Taliban units will be pursued and destroyed, but anti-Taliban areas will be rewarded with dollops of money.

British troops will not eradicate poppies, which is impossible, but eliminate the occasional shipment or middle-man (thereby making the crop even more valuable). Richards hopes this will bring the “lost” southern provinces over to Kabul’s side. He shrugs at how this can possibly work with just 3,300 British troops and some reluctant Canadians and Dutch. He is the boy on the burning deck.

The western idea that Kabul can, with a handful of foreign mercenaries, assert a control over Afghanistan that it has not enjoyed in history is bizarre. Such ideas gain currency only when foreign policy departs the national interest and good sense vanishes in clouds of international do-goodery.

Kabul is now a statelet crammed with the cosmopolitan staff of massed United Nations development agencies and 800 NGOs, many withdrawn from an unsafe hinterland. They are guarded by a garrison of 36 nations under a Nato umbrella, said to be operating with 71 different rules of engagement. They form an astonishing babble of adventurers, mercenaries, idealists and philanthropists. Their joking ambition is to create “not an Afghanistan run by Swedes but a Sweden run by Afghans”.

It is the sort of armchair interventionism ridiculed by Rory Stewart in his new book Occupational Hazards (reviewed in today’s Culture). As he picks his way across some mortar-strewn, bloodstained province in Iraq, he receives e-mails from Baghdad’s green zone requesting news of his gender awareness seminar and his democracy enhancement project.

Such is the raw material of Richards’s Afghan crusade, regarded by most observers as the West’s last attempt at constructive engagement in the region. He is answerable not to London but to Karzai and is desperate to downplay the significance of the Helmand operation in the south. All southern and eastern provinces straddling the border are awash in insurgency and instability. The most that any outside army can hope to achieve is to hold a few exemplary villages for a few exemplary days. Richards’s best bet is in the more friendly north.

Karzai is clearly distancing himself from the foreigners crowding his outer office. His coalition is stuffed with so many warlords, or “commanders”, that a 2005 UN report had to be suppressed for fear of revealing their record of torture, murder and worse. Last month he further infuriated the foreign community by appointing 13 provincial police chiefs who were openly known as criminals, drug runners and thugs. All were tribal nominees.

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