Pakistan has highlighted the hold it has over the US and Nato forces in Afghanistan by stopping their supply trucks from crossing the Afghan frontier. The ban is in retaliation for US helicopters making an attack on the Pakistani side of the border and killing three Pakistani soldiers.
The US is making a somewhat desperate attempt to close down the Afghan Taliban's bases on the Pakistani side of its 2,500km-long border with Afghanistan. The US military's hope of a year ago that a surge in troop numbers inside Afghanistan would turn the tide in the guerrilla war is fading fast. The Taliban have extended their grip in the north and west of the country. The one option left to America and its allies is to try to force the Pakistan army to act decisively against the Taliban in Pakistan.
It is not going to happen. The Pakistan military has become adept over the past decade at outmanoeuvring Washington on this issue. The Taliban were very much Pakistan's creation in the 1990s, though the relationship has been more distant since 9/11. The army has no interest in putting the Taliban permanently out of business and thereby lose Pakistan's main lever over America.
It is reasonable enough for Pakistan to claim that it could not close the Afghan-Pakistan frontier that runs through some of the toughest terrain on earth and is the same distance as between London and Moscow. If the US, with its massive airpower, cannot shut its side of the border, how come the Pakistani army is expected to be more effective on the Pakistani side? Whatever the direct role of Pakistan in sustaining the insurgency in Afghanistan, the bottom line is the same for the US and its allies now as it was for the Soviet Union in the 1980s. So long as the border with Pakistan remains at least partly open, the insurgents cannot be defeated.
One comic aspect of Pakistan shutting down Nato's supply line through the Khyber pass is that the Taliban themselves may not be too pleased to see the ban go on too long. A senior Pakistan officer told me last week in Islamabad that he reckoned that the Taliban received a large part of the $1,500 protection money paid by trucking companies for every one of the 1,000 or so trucks entering Afghanistan each day with supplies for US and Nato forces. This type of extortion may be as important to the Taliban's revenues as the heroin trade.
Local bandits have also been happy beneficiaries of the 80 per cent of supplies for foreign forces in Afghanistan which come through Pakistani ports and are then driven north to the border. These are supposedly non-lethal goods such as fuel, spare parts and clothing. But raids on warehouses in Peshawar by Pakistani security a few days ago discovered two Nato helicopters waiting for a buyer. Locals tell with some merriment of another looted container that turned out to be entirely filled with whisky bottles. Religiously inclined bandits briefly thought of destroying the cargo, but were swiftly convinced by fellow villagers that it would all be sold to non-Muslims.
David Cameron accused Pakistan of aiding the Taliban during his trip to India several months ago and was criticised for his lack of diplomacy. In this minor row the point was lost that the Pakistan and the Afghan insurgency are effectively joined at the hip. The Pakistani army may squeeze the Taliban but it will never squeeze them to death as the Americans want.
It will not do so because the Afghan Taliban are popular in Pakistan. Most Pakistani soldiers I spoke to were happy to fight the Pakistan Taliban, whom they denounced as parasitic on the reputation of their Afghan equivalents. They see the latter as Pashtun freedom fighters combating a foreign occupation and battling for a share in power against their non-Pashtun rivals such as the Tajiks, Uzbeks and Hazara. A Pakistani colonel commanding Pashtun troops on the border wondered how American and British troops could conciliate Pashtun villagers since "xenophobia is at the heart of Pashtun culture".
A second reason why the Pakistan military is unlikely to attack the Taliban is that we may be seeing the opening moves in the endgame in Afghanistan. The four main players are the US, the Afghan government, the Taliban and Pakistan. If the Pakistani army plays its cards right, then the outcome of any successful peace negotiations would be a power-sharing government in Kabul in which the Taliban would play an important role. Pashtun provinces would come under substantial Taliban control. Pakistan, with its strong influence over the Taliban, would be established as a regional power.
The American drone attacks on North Waziristan are at a level higher than at any time since they started in 2004. The killing of senior members of al-Qa'ida is triumphantly announced. But the border areas of Pakistan-Afghanistan are an unlikely area from which to mastermind a plot to bomb targets in Europe. There are checkpoints on all the roads in and out of the area. Strangers are closely watched. Jihadi fighters are much more likely to make their way overland to Somalia.
The mess which is American and British strategy in Afghanistan is exemplified by the ease with which the supplies of their forces can be choked off by Pakistan. The Pakistani army, which controls foreign and security policy in the country, is not going to kill off the Taliban at the request of the US. The Hamid Karzai government has less support than the communists at the time of the Soviet military withdrawal in 1988. The US and Britain are politically weak because they have such a feeble Afghan partner in Kabul and militarily weak because they cannot shut the Pakistan border. They have no choice but to negotiate.