Fourth, because, as we saw with the hysterical reaction to what U.S. troops thought was the routine burning of desecrated Qurans, Islam is the most powerful cultural and social force in the country. And the Taliban are the most deeply rooted in that faith.
Fifth, because nationalism is the most potent political current roiling nations from the Maghreb to Middle East to South Asia. And the Taliban have the causalities and credentials to prove they will fight forever to free their country of foreign influence.
A majority of Afghans surely wish the Taliban would not return, given the savagery of their previous rule and the desire of the Afghan people to be free to live their own lives according to their own interpretation of their faith.
Yet the Taliban have shown themselves willing to persist against huge odds, to fight and die in considerable numbers for the kind of country they wish to live in -- and the kind of regime they wish to live under.
Our allies have not remotely matched their zeal.
"A small body of determined spirits fired by an unquenchable faith in their mission can alter the course of history," said Mohandas Gandhi.
So, after a decade of war in Afghanistan, what have we accomplished, and at what cost? Some 2,000 U.S. dead, 16,000 wounded, hundreds of billions sunk, scores of thousands of Afghan dead. Al-Qaida was driven out a decade ago but is now in Pakistan, Yemen, Somalia, North Africa and Iraq.
The Taliban are gone from Kabul but may be coming back. And our hope of preserving what success we have had rests with Hamid Karzai.
"America has no designs beyond an end to al-Qaida safe havens," said Obama in Bagram. "Our goal is not to build a country in America's image, or to eradicate every vestige of the Taliban."
But if those are our goals, had we not achieved them all by early 2002? What, then, were we fighting for -- these 10 years?
If we had to do it all over again, would we?
The nation now seems not to think so. And the nation is right.