And when people try to drop out of the Delian League over time, Athens starts to exert itself. So the Delian League is really starting more and more and more into an Athenian empire. So once again, Athens proved itself, its navy proved itself to be very powerful in this war. Sparta's getting insecure. Athens doesn't listen to Sparta about this wall and decides to start building it. As Sparta's feeling even more insecure. Athens is starting to create this Delian League, which is really an Athenian empire, even more insecure.