Why is Afghanistan a quagmire?

In a word?  Pakistan.  Walter Russell Meade:

There is a flaming contradiction at the heart of President Obama’s Afghan war policy that threatens his strategy for safe withdrawal; the latest news from Pakistan suggests that the President now recognizes that something basic has to change.
Many readers find their eyes glazing over when it comes to yet more bad news from Pakistan, the “Islamic” republic which brings so little happiness to itself and its neighbors.  (One of life’s little mysteries: why more Muslims don’t demand that countries take the word “Islamic” out of their names until they cease to bring discredit upon it with their great honking failures of elementary justice?)
But depressing as the Pakistan news usually is, especially to those of us who know some of the idealistic and genuinely patriotic people in Pakistan who are working so hard to make things better, and who have a feel for the kind of place this beautiful country could some day become, you have to follow this story if you want to make sense of world news.  There are signs that US policy is moving toward a tipping point on Pakistan, one that would have major consequences for a lot of big issues, including the war in Afghanistan.

The President now seems to be facing up to the problem at the heart of his Afghan war strategy.  Withdrawing from Afghanistan requires building an acceptable (if far from perfect) future Afghan government that at the minimum won’t permit the country’s territory to be used as a basis for attacks against neighbors and the US and its allies.  But Pakistan, whose cooperation is necessary for that strategy to work, loathes and hates that outcome and is willing to do everything in its power to ensure that postwar Afghanistan looks very different.
This is not a little problem to be papered over with communiques, with Pakistani objections silenced by appropriately large and poorly supervised transfers of aid.  It is a basic strategic difference, a clash of interests, and if it cannot be overcome the US must find a new Afghan strategy.
If the Pakistanis don’t change their minds, the US must now look to secure its interests in postwar Afghanistan without Pakistan’s help and even over its determined opposition.  Pakistan’s plan for postwar Afghanistan (a country controlled by radical Islamists in a close relationship with Pakistan who are committed to jihad in South and Central Asia and elsewhere) would turn the country into a petri dish for terror plots and a magnet for deranged and violent fanatics from all over the world.  Preventing this outcome is why the US has been at war in Afghanistan for so long; securing that outcome is the chief strategic goal of a powerful wing of the somewhat fragmented and confused Pakistani national security system.

Except, what to do about it?  It is very difficult to supply forces in Afghanistan because of the landlocked nature of the country.  Without Pakistan's help it will be next to impossible.  Meade's take:

This means bringing India, Russia and Iran into the country, and winning at least tacit consent from China on the importance of a non-jihadi Afghanistan.  To certain strains of nationalist opinion among Pakistanis, this will feel like the ultimate betrayal.  Given that Pakistan has nuclear weapons and parts of its government are closely linked with terrorist groups already at war with the US, there is a potential for serious harm.  One is sorry to say that things are so bad that one hopes Pakistanis have no illusions about the consequences if Pakistani nukes end up in terrorist hands.
The US would still rather move on in Afghanistan with Pakistan rather than against it, but time and trust are running short.  It looks from the outside (and probably also looks this way in Islamabad) that the Obama administration is carefully and deliberately orchestrating pressure.  I suspect that the hardline Pakistanis, secure in their arrogance and contempt for an administration they believe is weak and poorly led, will be telling their colleagues that the President is bluffing and pushing for a policy of brinkmanship.  Push this guy and he steps back, they are saying.  He talks tough but backs down.

And we would have to bring Russia, Iran and China into it why?  They've done more to mess this up for us than help, because they see it as in their interests to mess it up for us.  That is why Pakistan is kissing up to China right now.

As I've said before: screw 'em all.  If the Paks and their friends are intent on making life difficult for us, pull out and and let India have at 'em.