Why Is The Delian League Successful

Explain how successful the Delian League was.
To know better about how successful the league was, it is good to know why the league has founded in the first place.
After some Greek city states including Athens encouraged and facilitate cities in Asia minor to rebel against Persia, The Persian empire had subdued the rebellions and then, to address the root of the problem decided to attack Greece.
From the two decades of Greco-Persian war, it was the Athens and her allies who came out victorious eventually. After the war, there was a discussion between the alliance about the continuation of the war against Persia. Some states like Sparta were against the war and believed the war is over however some others like Athens relied on extension of war against Persia.
Eventually the cities who were for the war, met in the holly island of delos and had formed the Delian league. They agreed to fund the league financially, mainly because of keeping and upgrading a strong navy fleet against Persia. All members had to give a specific level of tribute to the league treasury in a regular basis.
Gradually, Athens begun to take advantage of the league to her own benefits. Athens had changed the direction of the league from the defense force against Persia to imperial power of her own. Athens encouraged the other members
After the defeat in Egypt, Athens used the excuse of concern over Persian revenge and moved the treasury from neutral delos to Athene city. Now the treasury in Athene, the leaders of Athens had full control of the whole league wealth to their sole benefits. With that wealth Athenians had been enjoying a comfortable and luxurious life style. Any member of the league who was against the unfair policy of Athens and tried to leave the league, would be considered rebellious and subdued and punished by