The war that has resumed between the Pakistani Army and the Taleban in the northern mountains of Pakistan is not between two clearly defined sides, with clearly defined victory and defeat. It is, instead, an extremely complicated mixture of war and politics, in which episodes of extreme violence alternate with periods of negotiation.

One of those violent periods is resuming now. Barely two months after a peace deal with the Taleban to create a Sharia system in the Swat district, the army is back on the offensive. The Taleban overstepped an unwritten mark when they tried to extend their control into the district of Buner, barely 60 miles northwest of Pakistan's capital, Islamabad. The army chief, General Asfaq Kayani, stated clearly that a challenge to the existence of the Pakistani state would not be tolerated.

What will be tolerated is Taleban strength in the tribal areas of northwest Pakistan. As I discovered during a visit to the region last September, the level of support for them there is such that crushing them completely would take a huge campaign of repression.

As long as this conflict remains restricted to the mountains, in many ways the most important prize is not control of territory as such, but the support of the local population.

There are many reasons why this is so, and why even many Pakistanis who deeply oppose Taleban rule are also opposed to a tough military campaign against them. One is that the jihad of the Afghan Taleban against the US “occupation” of Afghanistan enjoys overwhelming public approval in northern Pakistan, at least to judge by my interviews on the streets and in the bazaars, and the Pakistani Taleban gain a great measure of prestige from their alliance with this jihad.

Another is that, with the exception of some of the higher courts, the Pakistani judicial system is such a corrupt, slow, impenetrable shambles that the Taleban's programme of Sharia enjoys a great deal of public support, at least in the Pashtun areas that I have visited. Finally, the security Establishment is determined to prevent Afghanistan becoming an ally of India, and continues to shelter parts of the Afghan Taleban as a long-term “strategic asset” against this threat.

In a way, however, you really have to know only one fact to understand what is happening: and that, to judge by my meetings with hundreds of Pakistanis from all walks of life over the past nine months, is that the vast majority of people believe that the 9/11 attacks were not an act of terrorism by al-Qaeda, but a plot by the Bush Administration or Israel to provide an excuse to invade Afghanistan and dominate the Muslim world.

It goes without saying that this belief is a piece of malignant cretinism, based on a farrago of invented “evidence” and hopelessly warped reasoning, but that is not the point. The point is that most of the Pakistani population genuinely believe it, even here in Sindh where I have been travelling for the past week; and the people who believe it include the communities from which the army's soldiers, NCOs and junior officers are drawn. Understand this, and much else falls into place.

After all, if British soldiers strongly believed that the war in Afghanistan was the product of a monstrous American lie, involving the deliberate slaughter of thousands of America's own citizens, would they be willing for one moment to risk their lives fighting the Taleban?

All the same, it is important not to exaggerate the extent of Taleban power. Whatever Hillary Clinton, the US Scretary of State, may say, there is no possibility at present of the Taleban seizing Islamabad and bringing down the state. In Punjab, the province with a majority of the country's population, there have been a number of serious terrorist attacks and a growth of Taleban influence, but as yet, nothing like the insurgency occurring among the Pashtun tribes. In the interior of Sindh, support for the Taleban is virtually non-existent.

In Karachi, Pakistan's greatest city by far, the situation is more complicated. The vast majority of Karachi's Pashtuns support the Awami National Party (ANP), the moderate secular nationalist party now ruling in the North West Frontier Province. However, a small degree of Taleban infiltration has helped to reignite simmering tensions between the Pashtuns and the Mohajir majority, made up of people whose families migrated from India at the time of independence, who are represented by the Muttahida Quami Movement (MQM) party.

In clashes between the MQM and Pashtuns last week 32 people were killed - the great majority of them Pashtuns. The city fears that a return of inter-ethnic rivalry could cause great economic disruption and tie down yet more Pakistani soldiers who are desperately needed to fight the Taleban in the north.

The danger to Pakistan is not of a Taleban revolution, but rather of creeping destabilisation and terrorism, making any Pakistani help to the US against the Afghan Taleban even less likely than it is at present.

Anatol Lieven is a professor in the War Studies Department of King's College London

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