A confederation of Greek city-states that was formed as a common defense against Persian aggression. Because it was deemed likely the invasion would take place by sea, Athens, the foremost sea power in Greece, was the leader of the league. Each of the member states submitted men and materials for the common defense. Eventually they moved away from sending troops and ships, sending monetary payments instead, which ultimately turned into tribute to Athens. By the time peace with Persia was finalized, all but 3 members of the league (there were over 200 members at one point) made their contribution in money. This turned the league from a program of common defense into one of strengthening Athens. From this time, until the defeat of Athens by Sparta, the states of the Delian League were essentially subject states of Athens, with members compelled to remain in the league by force. Upon Sparta's victory in the Peloponnesian war in 404 BC, the league disintegrated, but was reformed in 377 by those who feared Sparta's growing power. In 371 the group again became subjects of Athens, although Athens lacked the power to enforce its will. The league ceased to exist for the final time when Philip II of Macedonia defeated Athens in 338 BC.