[CSB]

Centrifugal Force is the force generated by an object spinning around a hub. The object wants to fly off into space.
Example: Swinging the proverbial bucket of water round and round over your head. The water won't fall out even when overhead because centrifugal force is pressing it outwards.

So why does't the bucket fly off into space? Because an equal and opposite force -- Centripetal Force -- exists to pull the bucket back. In this case the force is the muscles in your arm and hand. Let go with the hand, and off goes the bucket. Centripetal Force could just as easily be a rope under tension, or perhaps a strong magnet. For the earth and the moon (or the space station) centripetal force is gravity. The force opposite the centrifugal force is centripetal force.

So it would appear that the article postulates that the Crusaders, leaving Europe and "spinning out" over the Mid East, diluted their combat strength and left them vunerable to the long and weaker forces binding them to Europe (if only longer lines of communications); while the Muslims from the outlying desert sands had a centripetal force bringing them together around Jerusalem, generating combat power through several of the Principles of War such as Mass and Objective.