There is always a high turnover of generals in wartime. Some get replaced because they turn out to be no good at the job, but many others are changed because they have failed at a task that was beyond anybody's ability to accomplish.

They are fired, in other words, because the alternative would be to blame the person who gave them that impossible task. That certainly seems to be the case with General David McKiernan, the American commander in Afghanistan, who was appointed by Defense Secretary Robert Gates less than a year ago, when President Bush was still in power.

The specific event that caused McKiernan's dismissal may have been his recent admission that there is a "stalemate" in Afghanistan. But it was probably inevitable anyway, because Gates, who was retained from the Bush administration by President Obama, needed somebody to blame for the fact that the military situation in Afghanistan is worse than ever.

What's need is "fresh thinking, fresh eyes on the problem," said Secretary Gates, explaining why he was appointing General Stanley McChrystal to the job instead. So what should General McChrystal's fresh eyes see?

He could start by understanding that the United States is not fighting the Taliban in Afghanistan. It is fighting the entire Pashtun nation, some 30 million people, two-thirds of whom live across the border in Pakistan. That border has never really existed for the Pashtuns, who move freely across it in peace and in war.

The Taliban are entirely Pashtun in membership, and always were. When they ruled southern and central Afghanistan in 1996-2001, they were hated by the other ethnic groups (who never lost control of the north), and even by many Pashtuns. But the U.S. invasion effectively drove not just the Taliban but the Pashtuns in general from power, in a country that Pashtuns have dominated for several centuries.

To minimize U.S. casualties, the United States made an alliance with all the non-Pashtun ethnic groups of Afganistan (the "Northern Alliance") in 2001. There really was no American land invasion; it was the Northern Alliance that defeated the Taliban, with considerable assistance from American B-52 bombers. It was a clever strategy, but it perpetuated what was effectively an Afghan civil war between the Pashtuns (40 percent of the population) and all the other ethnic groups, Tajik, Hazara, and Uzbek.

It is warlords from those other groups who have controlled the Afghan government ever since. "The political, religious and economic mafia are all Northern Alliance people," says Daoud Sultanzoy, a member of parliament from Ghazni province, exaggerating only slightly. "Nobody outside the Northern Alliance is in the government." Except, of course, President Hamid Karzai, the token Pashtun, who is mockingly known as "the mayor of Kabul".

This is not a war about ideology, even if all the American and Taliban commanders insist that it is. The Pashtuns are fighting to regain at least a major share of power in Afghanistan, while the U.S. and other foreign troops are for all practical purposes allied to the other ethnic groups. That is why ALL the fighting is in the Pashtun-majority provinces.

There is no point in trying to win over Pashtun "hearts and minds". The war will only end when the Pashtuns regain a big share of the power at the centre (and the loot that comes with it). And no matter how fresh General McChrystal's eyes are, it's unlikely that he can deliver that.

Hamid Karzai has ensured his re-election as president in the elections in August by bribing or bullying his most serious challenger into withdrawing from the race, and choosing "Marshal Fahim" (Mohammed Qasim Fahim), a powerful and notoriously bloody Tajik warlord, as his first vice-president. The other vice-president, Karim Khalili, is, predictably, a Hazara.

Karzai's second term will be a reprise of his first: the same ethnic imbalance, the same rampant corruption and warlordism, the same combination of toadying to the foreigners who provide the cash-flow and occasional outbursts of nationalist resentment when U.S. air strikes kill too many innocent civilians. And McChrystal should ignore the air force's promises to do better: in counter-insurgency wars, air strikes always kill more civilians than combatants.

On top of everything else, the U.S. still insists on eradicating the poppy-growing that provides over half of the country's national income. Opium use is obviously a problem in Afghanistan— as one observer said, "If you applied a drug test to the Afghan army, three-quarters of them would be kicked out"—but burning farmers' fields leaves them no alternative source of cash income except fighting for the Taliban, who pay $200 a month.

The final thing McChrystal should understand is that "winning" or "losing" in Afghanistan makes almost no difference to U.S. security. The Taliban are not "outriders for al-Qa'eda", in the lazy formula used by State Department special envoy Richard Holbrooke.

The Taliban are an Afghan phenomenon with almost exclusively Afghan goals, and even if they should win absolute power after the U.S. leaves (which is unlikely), there is no reason to believe that they would send terrorists to attack the United States. Indeed, Osama bin Laden probably didn't even let them know in advance about the 9/11 attacks.

This war is not only unwinnable but unnecessary, and if David McChrystal understood all these things he wouldn't have taken the job. But he did take it, so he doesn't understand. Afghanistan is Vietnam for slow learners.

Gwynne Dyer's latest book, Climate Wars, was published recently in Canada by Random House.