Once the Persian menace had been removed, petty squabbling began amongst the members of the Hellenic League. Sparta, feeling that its job was completed, left the association, and Athens assumed domination of the league. Under the leadership of Themistocles and Kimon, Athens reformed the alliance into a new body called the Delian League. By using monetary contributions from other member states to build its own military forces, Athens essentially transformed the Hellenic League into its own empire.

In the 450s B.C., Pericles (ca. 495-429 B.C.), known as the greatest statesman of ancient Greece, laid the foundation of imperial rule. Athens set the level of tribute for the member states, which were now subject to its dictates, and it dealt harshly with failures to pay. Athens also began regulating the internal policy of the other states and occasionally garrisoning soldiers there. At its height in the 440s B.C., the Athenian Empire was composed of 172 tribute-paying states. Athens now controlled the Aegean.

The enormous wealth entering Athens from subject states financed the flourishing of democratic institutions, literature, art, and architecture that came to be known as the golden age of Athens. Pericles built great architectural monuments, including the Parthenon, to employ workers and symbolize the majesty of Athens. The four greatest Greek playwrights--Aeschylus, Aristophanes, Euripides, and Sophocles--wrote during the golden age.

In society and government, lower-class Athenians were able to improve their social position by obtaining land in the subject states. Pericles gave more governing power to bodies that represented the citizenship as a whole, known as the demos. For the first time, men were paid to participate in government organizations and sit on juries. Many states outside the empire felt quite threatened by the growth of Athens, creating a volatile situation in the mid-fifth century B.C.