What's the Deal with the Delian League?

 While studying the Ancient Greeks, I came across something quite interesting. During the Persian Wars and the time that preceded the First Peloponnesian War, interest groups were at the center of Athens and its policy. In this case, the interest group at hand wasn't one in the traditional sense, like one might think of when they refer to the NRA. Instead, this interest group was far more similar to NATO. It was known as the Delian League, and it was formed as a preventative measure against the inevitable Persian invasion in the future.

This group was quite large, consisting of most of the islands in the Aegean Sea and quite a few other Hellenic cities. Its goal was to create a force of Greeks that was enough to rival the Persians, so the selective incentive here was that by joining one would be protected against Xerxes and his foreign invaders. Protection was to the Delian League as a duffle bag is to the NRA. But soon, they realized that the Persians weren't coming back and that even if they did, Athens, the leader of the group, could handle it even without their tribute payments. In a sense, they realized that the duffle bag wasn't as valuable as the little flier had made it out to be. As a result, many islands, such as Naxos, tried to free ride and get the public good of protection without paying tribute. (Of course, this was free riding since they knew Athens wouldn't allow the Persians to enter and gain any Greek territory). Athens didn't love this and then forced membership, turning it into an Empire with taxes instead. Even back then, people hated free riders.