That's what Rory Stewart argues in the case of Afghanistan. Specifically, he takes issue with people like my man Barak Obama and Hillary Clinton, who say we should stop concentrating our military might in Iraq and use more of it in Afghanistan. Stewart's thesis is that there has been great progress in large parts of Afghanistan, that the areas that are now unstable are going to be that way for a number of years, but that putting concentrations of troops in will only make the situation worse.
He gives a couple of examples where greater NATO presence (British troops in one case, Dutch in the other) has been accompanied by a worsening security situation. Frankly, I am not convinced by these cases; it may be the constraints of the op-ed page, with a more-or-less strict word limit, but the mere fact that things got worse with more troops does not prove that putting in the additional forces was the cause or even a major cause for the change.
Still, Stewart has a provocative point. I think I can safely say that I was one of the few Americans who expressed concern over going into Afghanistan in the first place. I did so for historical reasons: for millenia, foreigners have invaded that land, and one after another they have suffered defeat and even disaster. I did not expect that the Afghans would welcome us any more than they did the Greeks, the Moguls, the British (who suffered some of their greatest colonial-era defeats at Afghan hands) or the Russians.
I have been agreeably surprised, in general, by the way we have been received in Afghanistan, but I believe that it is vital for us to make clear that we have no desire for a permanent military presence in that nation, and that we want the Afghans to govern themselves. Naturally, there are things we could do to help them, and forward our own policy. Paying opium growers for their crop--and assuring them that it will be destroyed if they sell to drug dealers--would be one step. Finding new crops, even if they need subsidies, to replace the opium poppy would be a later and better one.
There is one point on which I think Stewart is wrong. I heard a talk by Barney Frank a couple of months ago, and he argued that one of the things that is driving Afghans from us is the toll of civilians killed in air strikes. We are using air strikes, according to Barney (he's my congressman, and everyone in the district calls him Barney) because we have so much of our military tied up in Iraq that we must fight on the cheap in Afghanistan. Putting in more troops so that we do not have to use the imprecise weapon of air power, and so can reduce civilian casualties, would be a good thing. Provided that we can avoid alienating the local people with our troops on the ground.