(I've abridged his article for you in a much more succinct and sarcastic format, for your enjoyment):
Afghanistan is not the "Graveyard of Empires", as many claim. It was only a proximate cause for the fall of the Soviet Union, merely a total defeat for the British Empire (but not related to the loss of their empire), and a brutal campaign which claimed 80% of Alexander the Great's army, and resulted in little short-term Hellenic consolidation. This is largely because it's just the ideal fighting ground from insurgents, a logistical nightmare, ethnically fractured, and whose history as a nation-state ruled from a strong, centralized government Kabul is somewhat less than spectacular...most empires also find themselves cutting their losses and leaving because it produces little of value. But to call it the actual "Graveyard of Empires" is a bit extreme.
Seriously, though, read the actual article and not my snarky commentary on it, as it's quite interesting. One of the comments to the article brings up a great point about the relatively successful incorporation of Afghanistan into the Persian Empire, which is worth reading more on.