Nato is useless. It has failed to bring stability to Afghanistan, as it failed to bring it to Serbia. It just breaks crockery. Nato has proved a rotten fighting force, which in Kabul is on the brink of being sidelined by exasperated Americans. Nor is it any better at diplomacy: witness its hamfisted handling of east Europe. As the custodian of the west's postwar resistance to the Soviet Union's nuclear threat it served a purpose. Now it has become a diplomats' Olympics, irrelevant but with bursts of extravagant self-importance.

Yesterday's Nato ministerial meeting in Brussels was a fig leaf over the latest fiasco, the failure to counter the predictable Russian intervention in Georgia. Ostensibly to save Russian nationals in South Ossetia, the intervention was, in truth, to tell Georgia and Ukraine that they must not play games with the west along Russia's frontier. Nato, which Russia would (and should) have joined after the collapse of the Soviet Union, is now a running provocation along the eastern rim of Europe.

There was no strategic need for Nato to proselytise for members, and consequent security guarantees, among the Baltic republics and border states to the south. Nor is there any strategic need for the US to place missile sites in Poland or the Czech Republic. This was mere Nato self-aggrandisement reinforcing the lobbying of the Pentagon hawks.

These moves were bound to infuriate the hypersensitive Russians, and did. There is no point in western pundits saying that the thrust of Nato close to the Russian border is quite different from the cold war location of Soviet missiles in Cuba. It seems the same to Russian nationalists.

Nor is it any good pundits remarking that Russia's defence of Russian minorities in Georgia is quite different from Nato's intervention to defend the Kurdish minority in Iraq or the Albanian minority in Serbia. Again, that is just how it seems to Russia.

George Bush said earlier this month that "the age of spheres of influence is over". In that case why push that most potent sphere of influence, Nato, to the Russian border? And what of the sphere-of-influence theory that underpinned Bush's neoconservative plan to conquer the Muslim world for democracy?

The US's two greatest bugbears at present, Russia and Iran, both have grounds for feeling encircled by hostile forces. However badly they behave, they too are vulnerable to the politics of irrational fear. Both countries display the rudiments of democratic activity, with paranoia playing on pluralism.

The glib response of Nato's leaders has been hawkish, that the only thing "these people" understand is tough talk and big sticks. But that just apes Russia's attitude towards Georgia and Ukraine, which at least Russia has the power to enforce.

The west is not threatened by Russia. Turning its border into a zone of bluff and counter-bluff, so Nato can boast 10 extra flags outside its headquarters, has proved destabilising and provocative. Intelligence, like morality, is supposedly the tribute power should pay to reason. Russia is boorish and belligerent enough already. Why encourage it?

With Russia, Nato is playing with fire. In Afghanistan/Pakistan - which should always be yoked together - it is playing with dynamite. Here Osama bin Laden and Donald Rumsfeld must be laughing in unison: the former because Nato's conduct of the war against the Taliban has been a recruiting sergeant for al-Qaida in Pakistan; the latter because everything he said about nation-building has proved true. "Get in fast and get out fast" was his strategy, and he was right.

The fall of Pervez Musharraf might be good news for Pakistan's democrats. It is dreadful news for Nato's proconsuls in their fortified enclaves in Kabul. The likelihood of political turbulence in Pakistan can only increase the hold that pro-Taliban tribes have over the long frontier with Afghanistan and, with it, the certainty of an escalating war.

Nato's performance here has been dreadful. A half-hearted peacekeeper, it had displayed divided counsels, divided leadership and divided rules of engagement. It has reflected the view of the US general in Kosovo, Wesley Clark, that US units should never again be placed under international command. International command means no command at all.

A Pentagon report by General Barry McCaffrey, revealed last week, criticises the lack of command unity in Kabul. "Afghanistan is in misery," it says. "A sensible coordination of all political and military elements of the Afghan theatre of operation does not exist."

There is said to be a plan for a 12,000-strong reinforcement of US troops to stage a Baghdad-style "surge", outside the remit of Nato. The idea that the rural Taliban might be susceptible to the same handling as Iraq's urban militias may be senseless, but is on the cards. Such a surge would mean three rival armies - Afghan, Nato and American - roaming this troubled land, a gift to any enemy.

The newly triumphant coalition in Islamabad must long for the days when its Afghan backyard was quiet. The Taliban regime was funded by opium and the Saudis, and of no strategic (as opposed to terrorist) concern to the west. There were no US Predators bombing villages, no CIA phone-tapping, no suborned Pakistan intelligence officers, no outside interference. Pakistan's sphere of influence might not be to every taste, but it was roughly stable.

We shall now have the world's sixth largest country, and with an active nuclear arsenal, in internal turmoil because of a doomed Nato adventure on its border. Taliban units are operating freely throughout the south and east of Afghanistan and within miles of the capital, Kabul, flatly contradicting the mendacious spin of Nato spokesmen over the past two years.

Western governments seem never to learn. Counter-insurgency wars of this sort never work if they become drawn out. At best they leave broken, corrupted, failed states such as Lebanon and Kosovo - and, soon, Iraq. At worst they mean defeat. If ever America were walking into another Vietnam, it is now in Afghanistan, fast replacing Iraq as the mecca for every anti-western fanatic on earth.

Peace in Afghanistan might not matter over much. But its absence will grossly destabilise Pakistan, and that matters greatly. Is this to be another feather in Nato's cap?

simon.jenkins@theguardian.com