Every day new historical reminders appear beside the road: burnt-out lorries, abandoned vehicles hit by missiles and tankers that never made it to Kabul. The Taleban's noose is being drawn ever tighter around the capital. The tactics are identical to those used against the British in 1841 and against the Russians two decades ago: to cut supplies to the city by blocking the few vital arteries leading through the surrounding mountains. Gradually the Taleban have edged closer, and now hold territory only 20 miles southwest of the capital. The supply lorries are still running. But fear is growing, casualties are rising and Nato is looking hard and long at ways to defy an ominous historical precedent (see page 39).

There are about 70,000 foreign troops in Afghanistan, including 8,200 Britons, and commanders of the International Security Assistance Force (ISAF) insist that, with superior air support and logistics, this foreign army will never suffer the defeat inflicted on the British and the Russians. But their confidence is not always reflected in Western public opinion. The death of ten French soldiers in Sarobi, 30 miles along the Jalalabad road from Kabul, has shocked France. A poll shows that more than half those asked now want France to end its Afghan mission.

Luckily, President Sarkozy remains steadfastly committed to France's role in ISAF. So too is the political leadership in Britain and Canada, countries that have also suffered high casualties. They know that wavering would be fatal. The Taleban would be further emboldened. Disaffected Pashtuns would rally to the insurgency. Warlords would seize a chance to renounce any nominal allegiance to the Karzai Government. Drug production would increase still further. And the credibility and cohesion of Nato would be undermined, not just in Afghanistan but within Europe.

There needs, nevertheless, to be a reassessment of the challenges and responses. Much more than simply the authority of the democratically elected Government in Kabul is at stake. The threat of a failed state is manifest on both sides of the Pakistani border, where the Taleban and al-Qaeda now operate with impunity. India is not alone in seeing political and social breakdown in Afghanistan as a danger to its own security; so do all central Asian states struggling against Islamist insurgencies. The threat to the West is equally plain: were Afghanistan again to become a haven for ideological extremists, the resulting export of terrorism could have devastating consequences.

Nato must be clear that it is fighting in Afghanistan to protect its own freedoms. There needs to be greater coherence, more joint operations, common rules of engagement and a more robust understanding of the mission. The European contingents, especially, should look at the success of the US forces. Commanders have acquired considerable local expertise. Military engineers carry out the infrastructure projects essential to winning the hearts and loyalties of villagers who are otherwise easily swayed by Taleban denunciations of infidels in their midst. Britain's aid effort, by contrast, is uncoordinated and unprotected.

It is wishful to think that Nato can prevail by arms alone or without acknowledging historical precedent. But that precedent does not point only to defeat. It points to the vital need to rescue a country from its history.