Afghanistan is famously recognized as the centerpiece in "The Great Game," where Britain, Russia, the US and numerous other countries have sought vainly to establish political control for literally hundreds of years. The failures of, first, Genghis Khan, and, much later, the British and Russians to subdue the unruly peoples of Central Asia led to the description of Afghanistan as the "graveyard of empires."
The history of failed efforts to control Afghanistan is brilliantly described in Peter Hopkirk's 1994 book, The Great Game (Kodansha International). As Hopkirk presciently noted in the foreward to his book: "the collapse of the Soviet Union has tossed Central Asia back into the melting pot of history. Almost anything could happen there, and it would take a brave, or foolish, man to forecast what. But one thing seems certain. Central Asia, for good or for ill, is back once more in the thick of the news, and looks like staying there for a long time to come."
Given the history of "The Great Game," President Obama is well advised to be cautious about staying in Afghanistan at all, let alone deploying more troops there. But, as usual, the choice is not so simple for several reasons. For one, an unstable Afghanistan could, once again, become home to the same radical terrorist groups (and others) that attacked the US on 9/11. For another, Afghanistan's neighbor Pakistan is itself teetering on the brink of instability, posing an even greater potential danger to the region and the world simply because Pakistan is a nuclear power. If the US cuts and runs from Afghanistan, the implications for Pakistan and, potentially, for the US are parlous.
In other words, there are no first-best options for the US president in Afghanistan. Any choice he makes is sure to be roundly criticized, and with good reason. That is, ultimately, what it means to be president. I do not envy him the decision he must make.