The second phase of the Peloponnesian War begins in 414 BCE, when Sparta repulses a massive Athenian invasion of Sicily; Persia gives support to the Spartan cause.

By 411, the Athenian's Syracusan debacle and the subsequent renewal of war with Sparta as occasioned revolts in the Athenian empire and serious political turmoil at home.

Aided by Persian resources, Sparta becomes a naval power, and foments the rebellion of Athens's allies.

The Spartans move north from Chios to the Hellespont, gradually overcoming the Athenian navy despite effective countermeasures taken by Alcibiades and others. (This stage of the Peloponnesian war is called "Decelean" from the name of a town in Attica, Decelea, which Sparta fortifies—to the enormous cost of the Athenians.)

The Syracusan Greeks control southern Italy and eastern Sicily, while the Greeks of Massilia control the French coast.

Two important cities in Sicily, Dorian-Greek Selinus and Ionian-Greek (former Elymian) Segesta renew their rivalry

Selinus encroaches on Segestan land and defeats the Segestians in 416 BCE.

Carthage turns down their plea for help, but Athens responds to the Segestan plea.

A large Athenian military expedition to Sicily that takes place during the period from 415 BCE to 413 BCE (during the Peloponnesian War) results in a decisive Athenian defeat, and the complete destruction of the Athenian expeditionary force.

Two hundred ships and thousands of soldiers, an appreciable portion of the city's total manpower, are lost in a single stroke.

Athens' enemies on the mainland and in Persia are encouraged to take action, and rebellions break out in the Aegean.

The defeat proves to be the crucial turning point in the Peloponnesian War, though Athens will struggle on for another decade.

The disastrous Sicilian Expedition ushers in the final phase of the war, generally referred to either as the Decelean War, or the Ionian War.

In this phase, Sparta, now receiving support from Persia, supports rebellions in Athens' subject states in the Aegean Sea and Ionia, undermining Athens' empire, and, eventually, depriving the city of naval supremacy.

Selinus again defeats Segesta in 411 BCE.

This time, Segesta submits to Carthage, and a Carthaginian relief force sent by Hannibal Mago helps Segesta defeat Selinus the following year.

Carthage seeks to end the matter diplomatically while assembling a larger force.

After a round of diplomacy involving Carthage, Segesta, Selinus and Syracuse fails to bring about a reconciliation between Segesta and Selinus, Hannibal Mago sets out for Sicily with a larger force, triggering the Second Sicilian War between Syracuse and Carthage.

Representatives of Tissaphernes and of Pharnabazus, hereditary satrap of Dascylium in Hellespontine Phrygia, as well as ambassadors from Chios, …

Athens, having become entangled in the affairs of the Persian satrap Pissuthnes, who had revolted in 420 against his Achaemenid overlord, and subsequently with his natural son Amorges, sends mercenary help to Pissuthnes and perhaps to Amorges.

The Persian aristocrat Tissaphernes, dispatched by his king to Lydia, manages to incite a rebellion under Pissuthnes' Greek mercenaries, and achieving this offers negotiations.

Pissuthnes, upon his arrival at the place of the talks, is arrested, sent to Darius, and executed; Tissaphernes succeeds Pissuthnes as satrap of Lydia in about 415 BCE.

During his first years, he still must fight against Pissuthnes' son Amorges, who continues the struggle, possibly with Athenian help.

After the Athenian defeat at Syracuse, Darius, angered by the Amorges affair and determined to recover the Greek coastal cities of Asia Minor, which have been under Athenian control since 448, decides to back the Spartans.

The satraps of Asia Minor are ordered to collect overdue tribute.

As satrap of Lydia and Caria and general of the Achaemenid forces in Anatolia, Tissaphernes allies with Sparta against Athens in 413 and urges Athens’s colonies in Asia Minor to revolt.

…Clazomenae, and …

…Erythrae, invite the Spartans to carry the war across to the eastern Aegean.

This Sparta does, and in some long, drawn-out diplomacy, it agrees to abandon all claims to Anatolia as part of a deal for money and a fleet.

The playwright Sophocles is one of the ten commissioners who govern Athens from 413, following the disastrous Sicilian expedition.

Euripides produces his own interpretation of the curse on the House of Atreus with his version of Electra, produced in 413, which covers the same events but paints a more psychologically realistic portrait of the infamous matricide.

Perdiccas had left the Athenians by 417 BCE and joined the Spartan-Argive alliance.

Bowing to Athenian pressure just four years later, Perdiccas breaks with the Peloponnese, and aids Athens in their attack on Amphipolis.

He dies in 413 BCE, leaving his son Archelaus as heir.

Alcibiades meanwhile confirms his reputation with women (which the rich Athenian whom he had married appreciates only too well) by seducing the wife of the Spartan king Agis II, who is at Decelea with his army.