Periclean strategy
It was from the alliance's treasury that Pericles drew the funds necessary to enable his ambitious building plan, centered on the "Periclean Acropolis", which included the Propylaea, the Parthenon and the golden statue of Athena, sculpted by Pericles' friend, Phidias. In 449 BC Pericles proposed a decree allowing the use of 9,000 talents to finance the major rebuilding program of Athenian temples. Angelos Vlachos, a Greek Academician, points out the use of the alliance's treasury, initiated and executed by Pericles, as one of the largest embezzlements in human history; this misappropriation financed, however, some of the most marvellous artistic creations of the ancient world.

Samian War: The Samian War was one of the last significant military events before the Peloponnesian War. After Thucydides' ostracism, Pericles was re-elected yearly to the generalship, the only office he ever officially occupied, although his influence was so great as to make him the de facto ruler of the state. In 440 BC Samos went to war against Miletus over control of Priene, an ancient city of Ionia on the foot-hills of Mycale. Worsted in the war, the Milesians came to Athens to plead their case against the Samians.
When the Athenians ordered the two sides to stop fighting and submit the case to arbitration in Athens, the Samians refused. In response, Pericles passed a decree dispatching an expedition to Samos, "alleging against its people that, although they were ordered to break off their war against the Milesians, they were not complying".
In a naval battle the Athenians led by Pericles and nine other generals defeated the forces of Samos and imposed on the island an Athenian administration. When the Samians revolted against Athenian rule, Pericles compelled the rebels to capitulate after a tough siege of eight months, which resulted in substantial discontent among the Athenian sailors. Pericles then quelled a revolt in Byzantium and, when he returned to Athens, gave a funeral oration to honor the soldiers who died in the expedition.
Between 438 and 436 BC Pericles led Athens' fleet in Pontus and established friendly relations with the Greek cities of the region. Pericles focused also on internal projects, such as the fortification of Athens (the building of the "middle wall" about 440 BC), and on the creation of new cleruchies, such as Andros, Naxos and Thurii (444 BC) as well as Amphipolis (437–436 BC).

Personal attacks: Pericles and his friends were never immune from attack, as preeminence in democratic Athens was not equivalent to absolute rule. Just before the eruption of the Peloponnesian War, Pericles and two of his closest associates, Phidias and his companion, Aspasia, faced a series of personal and judicial attacks.
Phidias, who had been in charge of all building projects, was first accused of embezzling gold meant for the statue of Athena and then of impiety, because, when he wrought the battle of the Amazons on the shield of Athena, he carved out a figure that suggested himself as a bald old man, and also inserted a very fine likeness of Pericles fighting with an Amazon.
Aspasia, who was noted for her ability as a conversationalist and adviser, was accused of corrupting the women of Athens to satisfy Pericles' perversions. The accusations against her were probably nothing more than unproven slanders, but the whole experience was very bitter for Pericles. Although Aspasia was acquitted thanks to a rare emotional outburst of Pericles, his friend Phidias died in prison according to Plutarch; however, he is also credited with the later statue of Zeus at Olympia, therefore this is debated, and another friend of his, Anaxagoras, was attacked by the ecclesia for his religious beliefs.
Beyond these initial prosecutions, the ecclesia attacked Pericles himself by asking him to justify his ostensible profligacy with, and maladministration of, public money. According to Plutarch, Pericles was so afraid of the oncoming trial that he did not let the Athenians yield to the Lacedaemonians. Beloch also believes that Pericles deliberately brought on the war to protect his political position at home. Thus, at the start of the Peloponnesian War, Athens found itself in the awkward position of entrusting its future to a leader whose pre-eminence had just been seriously shaken for the first time in over a decade.

Peloponnesian War: The causes of the Peloponnesian War have been much debated, but many ancient historians lay the blame on Pericles and Athens. Plutarch seems to believe that Pericles and the Athenians incited the war, scrambling to implement their belligerent tactics "with a sort of arrogance and a love of strife". Thucydides hints at the same thing, believing the reason for the war was Sparta's fear of Athenian power and growth. However, as he is generally regarded as an admirer of Pericles, Thucydides has been criticized for bias against Sparta.

Prelude to the war: Pericles was convinced that the war against Sparta, which could not conceal its envy of Athens' pre-eminence, was inevitable if unfortunate. Therefore, he did not hesitate to send troops to Corcyra to reinforce the Corcyraean fleet, which was fighting against Corinth. In 433 BC the enemy fleets confronted each other at the Battle of Sybota and a year later the Athenians fought Corinthian colonists at the Battle of Potidaea; these two events contributed greatly to Corinth's lasting hatred of Athens. During the same period, Pericles proposed the Megarian decree, which resembled a modern trade embargo. According to the provisions of the decree, Megarian merchants were excluded from the market of Athens and the ports in its empire. This ban strangled the Megarian economy and strained the fragile peace between Athens and Sparta, which was allied with Megara. According to George Cawkwell, a praelector in ancient history, with this decree Pericles breached the Thirty Years' Peace "but, perhaps, not without the semblance of an excuse". The Athenians' justification was that the Megarians had cultivated the sacred land consecrated to Demeter and had given refuge to runaway slaves, a behavior which the Athenians considered to be impious.
After consultations with its allies, Sparta sent a deputation to Athens demanding certain concessions, such as the immediate expulsion of the Alcmaeonidae family including Pericles and the retraction of the Megarian Decree, threatening war if the demands were not met. The obvious purpose of these proposals was the instigation of a confrontation between Pericles and the people; this event, indeed, would come about a few years later. At that time, the Athenians unhesitatingly followed Pericles' instructions. In the first legendary oration Thucydides puts in his mouth, Pericles advised the Athenians not to yield to their opponents' demands, since they were militarily stronger. Pericles was not prepared to make unilateral concessions, believing that "if Athens conceded on that issue, then Sparta was sure to come up with further demands". Consequently, Pericles asked the Spartans to offer a quid pro quo. In exchange for retracting the Megarian Decree, the Athenians demanded from Sparta to abandon their practice of periodic expulsion of foreigners from their territory (xenelasia) and to recognize the autonomy of its allied cities, a request implying that Sparta's hegemony was also ruthless. The terms were rejected by the Spartans, and with neither side willing to back down, the two cities prepared for war. According to Athanasios G. Platias and Constantinos Koliopoulos, professors of strategic studies and international politics, "rather than to submit to coercive demands, Pericles chose war". Another consideration that may well have influenced Pericles' stance was the concern that revolts in the empire might spread if Athens showed itself weak.

First year of the war (431 BC): In 431 BC, while peace already was precarious, Archidamus II, Sparta's king, sent a new delegation to Athens, demanding that the Athenians submit to Sparta's demands. This deputation was not allowed to enter Athens, as Pericles had already passed a resolution according to which no Spartan deputation would be welcomed if the Spartans had previously initiated any hostile military actions. The Spartan army was at this time gathered at Corinth, and, citing this as a hostile action, the Athenians refused to admit their emissaries. With his last attempt at negotiation thus declined, Archidamus invaded Attica, but found no Athenians there; Pericles, aware that Sparta's strategy would be to invade and ravage Athenian territory, had previously arranged to evacuate the entire population of the region to within the walls of Athens.
No definite record exists of how exactly Pericles managed to convince the residents of Attica to agree to move into the crowded urban areas. For most, the move meant abandoning their land and ancestral shrines and completely changing their lifestyle. Therefore, although they agreed to leave, many rural residents were far from happy with Pericles' decision.