20 ! answer thoroughly ! what caused the delian league, and ultimately, athens to fail?

The Delian League was an organization made up of Greek city-states of which Athens is the leader and the organization was made so that the whole league and it's members could end Persian rule.   
The organisation together of more than 300 urban areas would in the long run be so ruled by Athens that, in actuality, it developed into the Athenian domain. Athens turned out to be progressively more forceful in its control of the union and, now and again, obliged participation by military power and constrained proceeded with tribute which was as cash, boats or materials. Following Athens' thrashing on account of Sparta in the Peloponnesian War in 404 BCE the League was broken down.