Pericles made his first military excursions during the First Peloponnesian War, which was caused in part by Athens' alliance with
Megara and
Argos and the subsequent reaction of Sparta. In
454 BC he attacked
Sicyon and
Acarnania. He then unsuccessfully tried to take Oeniadea on the Corinthian gulf, before returning to Athens. In 451 BC, Cimon is said to have returned from exile and negotiated a five years' truce with Sparta after a proposal of Pericles, an event which indicates a shift in Pericles' political strategy. Pericles may have realized the importance of Cimon's contribution during the ongoing conflicts against the Peloponnesians and the
Persians. Anthony J. Podlecki argues, however, that Pericles' alleged change of position was invented by ancient writers to support "a tendentious view of Pericles' shiftiness".
Plutarch states that Cimon struck a power-sharing deal with his opponents, according to which Pericles would carry through the interior affairs and Cimon would be the leader of the Athenian army, campaigning abroad. If it was actually made, this bargain would constitute a concession on Pericles' part that he was not a great strategist. Kagan believes that Cimon adapted himself to the new conditions and promoted a political marriage between Periclean liberals and Cimonian conservatives.
In the mid 450s the Athenians launched an unsuccessful attempt to aid an Egyptian revolt against Persia, which led to a prolonged siege of a Persian fortress in the
Nile Delta. The campaign culminated in a disaster on a very large scale; the besieging force was defeated and destroyed. In 451–450 BC the Athenians sent troops to
Cyprus. Cimon defeated the Persians in the
Battle of Salamis, but died of disease in
449 BC. Pericles is said to have initiated both expeditions in Egypt and Cyprus, although some researchers, such as Karl Julius Beloch, argue that the dispatch of such a great fleet conforms with the spirit of Cimon's policy.
Complicating the account of this complex period is the issue of the
Peace of Callias, which allegedly ended hostilities between the Greeks and the Persians. The very existence of the treaty is hotly disputed, and its particulars and negotiation are equally ambiguous. Ernst Badian believes that a peace between Athens and Persia was first ratified in 463 BC (making the Athenian interventions in Egypt and Cyprus violations of the peace), and renegotiated at the conclusion of the campaign in Cyprus, taking force again by 449–448 BC. John Fine, on the other hand, suggests that the first peace between Athens and Persia was concluded in 450–449 BC, as a result of Pericles' strategic calculation that ongoing conflict with Persia was undermining Athens' ability to spread its influence in Greece and the
Aegean. Kagan believes that Pericles used
Callias, a brother-in-law of Cimon, as a symbol of unity and employed him several times to negotiate important agreements.
In the spring of 449 BC, Pericles proposed the Congress Decree, which led to a meeting ("Congress") of all Greek states in order to consider the question of rebuilding the temples destroyed by the Persians. The Congress failed because of Sparta's stance, but Pericles' real intentions remain unclear. Some historians think that he wanted to prompt some kind of confederation with the participation of all the Greek cities, others think he wanted to assert Athenian pre-eminence. According to the historian Terry Buckley the objective of the Congress Decree was a new mandate for the
Delian League and for the collection of "phoros" (taxes).
During the
Second Sacred War Pericles led the Athenian army against
Delphi and reinstated
Phocis in its sovereign rights on the
oracle. In
447 BC Pericles engaged in his most admired excursion, the expulsion of barbarians from the Thracian peninsula of
Gallipoli, in order to establish Athenian colonists in the region.
At this time, however, Athens was seriously challenged by a number of revolts among its allies (or, to be more accurate, its subjects). In
447 BC the oligarchs of
Thebes conspired against the democratic faction. The Athenians demanded their immediate surrender, but, after the
Battle of Coronea, Pericles was forced to concede the loss of Boeotia in order to recover the prisoners taken in that battle. With Boeotia in hostile hands, Phocis and Locris became untenable and quickly fell under the control of hostile oligarchs. In
446 BC, a more dangerous uprising erupted.
Euboea and
Megara revolted. Pericles crossed over to Euboea with his troops, but was forced to return when the Spartan army invaded
Attica. Through bribery and negotiations, Pericles defused the imminent threat, and the Spartans returned home. When Pericles was later audited for the handling of public money, an expenditure of 10
talents was not sufficiently justified, since the official documents just referred that the money was spent for a "very serious purpose". Nonetheless, the "serious purpose" (namely the bribery) was so obvious to the auditors that they approved the expenditure without official meddling and without even investigating the mystery. After the Spartan threat had been removed, Pericles crossed back to Euboea to crush the revolt there. He then inflicted a stringent punishment on the landowners of
Chalcis, who lost their properties. The residents of
Istiaia, meanwhile, who had butchered the crew of an Athenian
trireme, were uprooted and replaced by 2,000 Athenian settlers. The crisis was brought to an official end by the Thirty Years' Peace (winter of 446–
445 BC), in which Athens relinquished most of the possessions and interests on the Greek mainland which it had acquired since 460 BC, and both Athens and Sparta agreed not to attempt to win over the other state's allies.