The Prime Minister tells us that our aims in Afghanistan are clear, justified, realistic and achievable. Three-quarters of the terrorist plots against us, he says, originate in the mountains between Afghanistan and Pakistan. He wants the Afghans to deal with this threat themselves, so that we can bring our soldiers home.

So we and our allies are training the army and police, improving "governance", tackling corruption and drugs, promoting education, health care and economic development. We will thus, says the Foreign Secretary, unite "key players behind shared goals - al-Qaeda kept out, the different tribal groups kept onside, and the neighbours prepared to play a constructive role". All this, alas, is management-speak, with no obvious link between cause and effect.

Perhaps Gordon Brown's London conference on 28 January will cast a clearer light on these hugely difficult issues. History is not necessarily a reliable guide to action. Circumstances change, and so do outcomes. But ignorance of history is a bad basis for policymaking. The debate about Afghanistan is contaminated with myth and illusion. One is that Afghanistan is the graveyard of empires, and that Nato is about to go the same way as the Russians and the British in the 19th century. That is too simple. In a purely military sense, the British won their wars in the 19th century and the Russians won theirs in 1979-89. It was the surrounding politics that went wrong.

For the British, the history of Afghanistan is a compound of jolly stuff about the Great Game and self-righteous stuff about dastardly Russian interference in places that were rightly our exclusive business. The differences are fewer than we like to think. Both Britain and Russia were driven by the same motives: the promotion of trade and the security of their imperial frontiers, justified by ideas of glory and the notion of a "civilising mission". Both gained their ends through diplomacy, bribery, deceit, intrigue, treachery and ruthless force. Each was paranoid about the other: the British thought that the Russians were out to get their Indian territories, the Russians that the British wanted to control central Asia. Neither seriously entertained such unpromising projects, although hotheads on both sides occasionally came up with wild schemes.

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