When in the summer of 479 the teenaged Pericles finally learned of the allies' astonishing victory over the Persians at Plataea, he could rejoice for his city-state and Greece though worrying about his father. Xanthippus was still away from home, commanding the Athenian warships in the allied fleet that sailed east across the Aegean Sea to respond to the plea of the Greeks in Ionia to free them from the Persian Empire. Now that the allied coalition had repulsed the great invasion of central Greece, the Ionians began to hope the momentum of that victory could be leveraged to force their release from the Great King's control. This continuation of hostilities with the Persians was to have a monumental significance for the history of Athens and the career of Pericles, as alluded to before, because it led to the beginning of what scholars today call the Athenian Empire.

Since the Persian commanders on the Ionian coast in 479 decided their fleet was inadequate to confront the Greek alliance at sea, they disembarked their men onto the Mycale peninsula, opposite the island of Samos. The Greeks followed them onto the land, crushing their opponents in a fierce battle in which the Athenians won the prize as the best fighters by punching through the center of the enemy line. Xanthippus' reputation for military leadership soared as a result. Among the spoils seized by the victors were chests spilling over with valuables; the Persians always took a store of treasure along on their military expeditions. The Greeks were learning that success in battle against them could be lucrative.

The Greek allies next held a conference on the island of Samos just off the coast of Ionia to debate the fate of the Greeks who were pleading for liberation. The Peloponnesians, headed by the Spartans, made the startling proposal that the Ionians should be forced to evacuate their homes and abandon their land to the Persians. It seemed impossible to defend this region forever, went the Spartan argument, and the Ionians could be resettled in the west in territories that would be seized from Greeks who had Medized in the Persian Wars. Those traitors would be punished by being expelled to fend for themselves as homeless refugees.