Afghanistan, in its present incarnation, is an artificially created and relatively young state. For most of its history, its government did not need great legitimacy, since the state center was relatively weak and legitimacy was primarily focused at the kalay (or village) level. Legitimacy of the central government, perhaps because of the substantial autonomy of the countryside, was primarily based on having a generally-accepted royal family whose influence extended little beyond Kabul in normal times, and indirect rule through provincial governors and district administrators to represent the capital in remote regions.
Afghans vote (and rig votes) based on their ethnicity and there is no real national government.
This is basically what I argued for nearly a decade ago before the surges:
The end result in Afghanistan, if all goes well, will be a nominal national government that controls the capital region and reigns but does not rule local tribes and which actually helps the locals a bit rather than sucking resources from the locals, who in turn do not make trouble for the central government or allow their areas to be used by jihadis to plan attacks on the West. We press for reasonable economic opportunities, with bribes all around (I mean, foreign aid), to keep a fragile peace.
And we stick around this time, unlike after the Soviets left Afghanistan when we ignored the place, for a generation or two to see if we can move Afghanistan into the 19th century (hey, let's not get ahead of ourselves).
I based that on the belief that "Afghanistan" is a geographic and not a political term. A decade of effort hasn't changed that fact.
And apparently we also haven't empowered local authority. In the past I thought we were heading that way with our support for local defense forces, which I thought would be the basis for local authority (and legitimacy). I was wrong about that.
As the authors of that article argue, the US needs to build the basis of legitimacy that have been wrecked by generations of war that doesn't rely on a "national" government that cannot have legitimacy. And fight corruption, of course. Which I often drone on about.
Although I reject the notion that America lost an opportunity to pretend we won and get out after our forces killed Osama bin Laden. Since when is strategy about pretending to win?
If the Taliban would go away, a weak national government could survive. Our strategy seems to be about getting the Taliban to agree to that and so far they don't seem to be interested. We hope that military punishment will provide the motivation. But as long as Taliban leadership has a sanctuary in Pakistan can we kill enough of the foot soldiers to persuade the leaders to make peace?
UPDATE: Strategypage looks at Afghanistan, with the information that while the government has about 300,000 security forces the Taliban have 60,000. It is unclear if the Taliban total means full timers or includes part-timers. The Taliban endure a much higher rate of casualties than government forces.
Also, the real problem in Afghanistan remains Pakistan, which is increasingly a jihadi-influenced nuclear weapons state.
UPDATE: Trump will order half of our 14,000 troops to leave Afghanistan? So soon after we built up troops a bit, expanded our efforts, and convinced allies to add troops? That's a mistake. Bigly. Our allies will no doubt pull out some of their forces, too.
But Pakistan--which controls the Taliban and works hard to kill Indians--will be delighted that their pet Taliban will be emboldened and strengthened. The only thing I will say in defense of the reported decision--despite the optics that will at least temporarily reduce the morale of Afghan forces--is that if we have alternate ways of providing support to Afghan forces that pulling out troops doesn't have to be a disaster.
Afghanistan's president says this won't be a problem. But he'd have to say that, wouldn't he? We'll see what the details are.
As I said when Obama ordered US troops out of Iraq in 2011, the decision doesn't guarantee disaster, but it increases the chances of disaster.