Britain's Prime Minister Tony Blair has provided the most explicit statement so far of the objectives of US and British military action in Afghanistan. He has said Osama bin Laden and his associates have to be brought to justice and their network destroyed. Afghanistan must also cease to harbour terrorism. He also implied that the Taleban regime in Afghanistan has to be overthrown. It is difficult to imagine bin Laden and his associates either surrendering, or being brought to stand trial for the September 11 bombings and the earlier terrorist attacks they are wanted for. Bin Laden has been a wanted man since the bombings of the US embassies in East Africa in 1997, but has successfully evaded capture. Having failed to bring him to trial so far, it is realistic to assume that the aim of the military action will be to destroy him as well as his network. This is likely to be achieved by British and US special forces, aided perhaps by the anti-Taleban Northern Alliance. Given the nature of the terrain and the patchy intelligence on where bin Laden might be, this is likely to be a fairly long-drawn-out campaign. What is not clear is how the Taleban is to be dislodged. Britain and the United States have lined up an impressive array of military firepower, but this is not enough to invade Afghanistan and remove the Taleban. The best bet is to strengthen the Northern Alliance and give it the means to fight the Taleban. This strategy requires that Pakistan withdraw its support from the Taleban. The US has persuaded President Pervez Musharraf that it is in his country's interest to disassociate itself from the Kabul regime, and Mr Blair is due in Pakistan to press home the message. It is important to realise that neither of these two objectives - capturing bin Laden and overthrowing the Taleban - can be achieved quickly. There is a real danger of the military operation degenerating into a lengthy guerilla war of the kind the Soviet Union was sucked into in Afghanistan. This will spread instability to other countries in the region under pressure from religious fundamentalists. One can only hope for a quick end to the conflict.