Harpseal rules!
History has a place in all this, as does Islamic prophecy. Osama bin Laden did not choose to hide out in Afghanistan because he necessarily liked that part of the world. Nor was it because he kind of nominally fought the Russians there. In fact the Arabs, like bin Laden, did little fighting against the Russians. Even now many Afghani fighters look on them as interlopers.
BUT Osama bin Laden understands that, as one historian related, "dying by the thousands to defend the only nation in the world that is actually run by some form of Islamic law (the Shari'ah) they will come and they will die. Not just from Afghanistan and Pakistan but as far afield as Indonesia, Malaysia, the Gulf, Central Asia, Northwest Africa, etc. They did it once before, they will do it again."
Afghanistan has special significance to the world of militant Islam. It was once called Khurasan, along with parts of Iran and Pakistan. Muhammad said: "If you see the black flags coming from Khurasan, join that army, even if you have to crawl over ice, for that is the army of the Imam al-Mahdi and no one can stop that army until it reaches Jerusalem." That is one reason Osama bin Laden chose it as his base, or al-Qaida.
The fundamentalists in the Muslim world are waiting for the prophecy of Muhammad to be fulfilled. Muslims will come and fight because Khurasan (Afghanistan) cannot fall. Whether Shi'a or Sunni, just as certain millennial Christians await the coming of Christ the Muslim world of a certain bent believes it is on the verge of the return of the a precursor of the end times, and that is Imam al-Mahdi.
Now, anyone got a source on Diane Alden's quotation?
4) The Prophet (PBUH and HF) said: "We (I and my family) are members of a household that Allah (SWT) has chosen for them the life of the Hereafter over the life of this world; and the members of my household (Ahlul-Bayt) shall suffer a great affliction and they shall be forcefully expelled from their homes after my death; then there will come people from the East (see above hadeeths that say this army will come from Khorasan modern day Iran) carrying black flags, and they will ask for some good to be given to them, but they shall be refused service; as such, they will wage war and emerge victorious, and will be offered that which they desired in the first place, but they will refuse to accept it till they pass it to a man from my family (Ahlul-Bayt) appears to fill the Earth with justice as it has been filled with corruption. So whoever reaches that (time) ought to come to them even if crawling on the ice/snow since among them is the Vice-regent of Allah (Khalifatullah) al-Mahdi."
References:
Sunan Ibn Majah, v2, Tradition #4082,
The History Tabari
al-Sawa'iq al-Muhriqah, by Ibn Hajar, Ch. 11, section 1, pp 250-251