Athens' Mercenary Military

I just wanted to bring attention to something that I thought was an interesting fact raised by Thucydides in what almost seemed like a throw away line.  He very quickly mentions that most of Athens' military power was mercenary.  I just think that it is interesting that they were able to maintain control of the Delian League as an empire without even really using its own sailors.  The fact that it not only controlled a large fleet that the other nations were paying for, but that it maintained a large fleet that was only loyal to Athens because of the money it was giving them, not because of their alliance to their city-state.  I didn't see any explanation of how they did this, but I'm guessing that there was political manipulation of some type like Athens providing the triremes, but using the Delian treasury to pay for mercenaries and making sure that all of the ships have people from a mixture of different city-states or possibly they maintained one of the largest single navies and because of that any resistance even by the much larger foreign navies would have to be well organized (although I think the previous reading said Samos had the single largest navy, so I doubt that that would be the whole explanation,) or maybe Athens' economy was simply large enough to dominate the mercenary business even if some of the states rebelled, and then it just used all of the other incomes to solidify its holdings.  The main thing that I find interesting about this is even without a huge military how did Athens rise from being some of the main leaders of this league (even the undisputed single most important state) to the leader of the this league.  How without a huge military did it rise from being first among equals to the center of an empire.