What does "spokes" mean in this context?
The reference to the 'Airfield' in your sentence indicates that this is probably meant in the Airline Hub sense, which is a specific implementation of the spoke-hub distribution paradigm.
In the above diagram, Denver is a hub; Los Angeles is another hub. Both have spokes radiating from them.
The definition of "metal bars on a bicycle wheel" is correct.
The article is using a wheel symbolically. Picture Kabul/Bagram Airfield centrally located (the bicycle hub) with spokes radiating out from the hub.