By NICHOLAS D. KRISTOF

The United States was born of our ancestors’ nationalistic resentment of a foreign power whose troops we saw as occupiers, not protectors. The British never fathomed our basic grievance — this was our land, not theirs! — so the more they cracked down, the more they empowered the American insurgency.

We have been similarly oblivious to the strength of nationalism in Afghanistan and Pakistan, particularly among the 40 million Pashtuns who live on both sides of the border there. That’s one reason the additional 21,000 troops that President Obama ordered to Afghanistan earlier this year haven’t helped achieve stability, and it’s difficult to see why 40,000 more would help either.

American policy makers were completely blindsided in recent weeks by outrage in Pakistan at the terms of our latest aid package — and if we can’t even hand out billions of dollars without triggering nationalistic resentment, don’t expect a benign reaction to tens of thousands of additional American troops.

We have been fighting in Afghanistan for twice as long as we fought in World War II, with a current price tag estimated to be more than $60 billion a year. Standard counterinsurgency ratios of troops to civilians suggest we would need 650,000 troops (including Afghans) to pacify the country. So will adding 40,000 more to the 68,000 already there make a difference to justify the additional annual cost of $10 billion to $40 billion, especially since they may aggravate the perception of Americans as occupiers?

I’ve been fascinated by Pashtuns ever since I first sneaked around the tribal areas as a university student, hiding in the luggage on tops of buses. My interviews in recent years with Pashtuns in both Afghanistan and Pakistan leave me thinking that we profoundly misunderstand the nature of the insurgency.

Some Taliban are fundamentalist ideologues who will fight us to the death. But others become fighters because they are paid to do so, because a tribal elder suggests it, because it gives them an excuse for traditional banditry, because American troops killed a cousin, or because they resent infidel forces in their land.

When Pakistani troops enter Pashtun areas, the result has sometimes been a backlash that helps extremists. If Pashtuns react that way to Punjabis, why do we think they will react better to Texans?

Indeed, modern Pashtun history is, in part, one of backlashes against overambitious modernization efforts that lacked local “buy-in.”

The American military has become far more sensitive to Afghan sensibilities in the last few years, and there are some first-rate commanders on the ground who cooperate well with local Pashtun leaders. That creates genuine stability. But all commanders cannot be above average, and a heavier military footprint almost inevitably leads to more casualties, irritation and recruitment for the Taliban.

One of the main arguments for dispatching more troops is the terrorist threat from Al Qaeda. But Steven Simon, a National Security Council official in the Clinton years who is now a terrorism expert at the Council on Foreign Relations, notes that there may be more Al Qaeda fighters in Pakistan, Yemen and perhaps Somalia than in Afghanistan.

“I’m skeptical that the war in Afghanistan is going to solve the Al Qaeda problem,” he said.

That’s not to say we should pull out, and it’s a false choice to suggest that we should either abandon Afghanistan or double down. A pullout would be a disastrous signal of American weakness and would destabilize Pakistan.

My suggestion is that we scale back our aims, for Afghanistan is not going to be a shining democracy any time soon. We should keep our existing troops to protect the cities (but not the countryside), while ramping up the training of the Afghan Army — and helping it absorb more Pashtuns to increase its legitimacy in the south. We should negotiate to peel off some Taliban commanders and draw them over to our side, while following the old Afghan tradition of “leasing” those tribal leaders whose loyalties are for rent. More aid projects, with local tribal protection, would help, as would job creation by cutting tariffs on Pakistani and Afghan exports.

Remember also that the minimum plausible cost of 40,000 troops — $10 billion — could pay for two million disadvantaged American children to go to a solid preschool. The high estimate of $40 billion would, over 10 years, pay for almost half of health care reform. Are we really better off spending that money so that more young Americans could end up spilling their blood in Afghanistan without necessarily accomplishing much more than inflaming Pashtun nationalism?