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.)

Mediterranean Southwest Europe (417–406 BCE): Sicilian Conflicts and Peloponnesian Reverberations

The era 417–406 BCE in Mediterranean Southwest Europe is marked by heightened tensions and pivotal conflicts in Sicily influenced by wider Greek geopolitical dynamics, ongoing developments within the Roman Republic, and sustained interactions among Carthaginians, Greeks, and indigenous populations across the broader region.

Sicilian Rivalries and the Athenian Expedition

The enduring rivalry between two significant Sicilian cities, Dorian-Greek Selinus and Ionian-Greek Segesta, escalates dramatically during this period. In 416 BCE, Selinus defeats Segesta, seizing its territory and prompting Segesta to appeal for external aid. Initially turned away by Carthage, Segesta successfully solicits assistance from Athens, setting in motion a substantial Athenian military intervention—the infamous Sicilian Expedition (415–413 BCE).

The Sicilian Expedition results in catastrophic failure for Athens. Facing the formidable defenses of Syracuse, Athens suffers a devastating defeat, losing two hundred ships and thousands of soldiers—crippling its military power and dramatically shifting the balance of the Peloponnesian War. This defeat emboldens Sparta and its Persian allies, marking a decisive turning point against Athenian dominance in the Mediterranean.

Second Sicilian War: Carthage and Syracuse

Following another defeat at the hands of Selinus in 411 BCE, Segesta submits to Carthaginian authority, significantly shifting local allegiances. Carthage, now actively involved, dispatches Hannibal Mago to aid Segesta, leading to a decisive victory against Selinus in 410 BCE. Attempts at diplomatic resolution between Carthage, Segesta, Selinus, and Syracuse fail, culminating in Hannibal Mago’s larger military expedition to Sicily and initiating the Second Sicilian War between Carthage and Syracuse.

Roman Republic: Institutional Reforms and Alliances

Amid regional turmoil, the Roman Republic undergoes notable institutional developments. Rome's social structure evolves as the tribunus plebis—tribune of the plebeians—gains prominence, significantly enhancing plebeian representation in governance. The formation of the Foedus Cassianum in 493 BCE, an alliance of mutual defense between Rome and the Latin League, continues to strengthen Roman political and military alliances, enabling Rome to consolidate influence in central Italy despite external conflicts and internal social challenges.

Artistic and Cultural Developments

The Etruscans, although facing political and military pressures, continue to flourish artistically. Fine Etruscan metalwork and sculpture—exemplified by iconic works like the bronze Capitoline She-Wolf—remain prominent, illustrating ongoing cultural sophistication and technical excellence in artistic production. Such works underscore the enduring cultural legacy of the Etruscans, even as their political dominance wanes.

Broader Regional Dynamics

Throughout Mediterranean Southwest Europe, indigenous populations, Carthaginians, Greeks, and Romans engage in complex interactions shaped by trade, alliances, and military confrontations. The power struggles in Sicily reflect broader shifts across the Mediterranean, highlighting how local conflicts can ripple through wider geopolitical landscapes. Carthaginian involvement in Sicily particularly underscores growing Carthaginian influence in western Mediterranean politics and commerce.

Legacy of the Era

The era 417–406 BCE significantly shapes the geopolitical and cultural landscape of Mediterranean Southwest Europe. The disastrous Athenian defeat in Sicily redefines Greek political dynamics, Carthaginian assertiveness in Sicily reshapes regional power balances, and Roman internal developments strengthen the foundations of republican governance, setting the stage for further expansion and regional influence.

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.

Sicily has always been prone to tyranny and political instability, partly because the island is threatened by potentially hostile neighbors ready to encroach and partly because there is a large population of non-Greek indigenous inhabitants such as the Sicel forces mobilized in mid-century by Ducetius.

Polis life has never struck deep enough roots, and populations tend to be mixed and are too often transplanted.

Immediately after the severe defeat of Athens by the Spartans and their allies at Cyzicus.

a radical democracy had been installed in Syracuse, at the instigation of an extremist called Diocles.

The leader of the moderate democrats, Hermocrates, had in held the position of admiral during the battle.

As a result, Hermocrates, who happens to be absent at the time, is banned "in absentia" in 410.

(Hermocrates, who will not return to Sicily until 408 BCE, will die in a street fight after a failed coup in Syracuse in 407 BCE.

Carthage goes to the help of Segesta, an ally in Sicily, in 409 BCE and turns the war into one of revenge for the earlier defeat of Hamilcar's forces at Himera in 480 BCE.

Hannibal, son of Gisgo, grandson of Hamilcar, and shofet of Carthage in 410 BCE, reasserts Carthaginian power in Sicily by invading the island with an army of one hundred thousand men.

The Carthaginians destroy Selinus; the city's walls are razed, and only twenty-six hundred of its inhabitants escape. (Selinus, although repopulated as a Carthaginian tributary, will never truly recover.)

Hannibal next besieges Himera, where his grandfather had met his death.

The Carthaginian forces enter the city-state in 409, plunder it, and permanently destroy it before departing.

In the process of this conquest Hannibal is said to have killed some three thousand prisoners of war, reportedly as revenge for the defeat his grandfather suffered in the Battle of Himera seventy years before.

The exiled Hermocrates, in attempting to force his way back to Syracuse, he is killed in a street fight during the winter of 408-407 in an attempt, so his enemies say, to establish a tyranny.

Seven troubled years have followed the Athenian surrender in 413.

For most of this period, there has been war with Carthage and internal convulsions that Carthage constantly seeks to exploit.

Hermocrates had plundered Carthaginian possessions in Sicily from Selinus after 408 BCE, and in response Carthage sends an army to Sicily under Hannibal Mago and Himilco II of the Magonid family, which faces a coalition of Sicilian Greeks under the leadership of Syracuse.

The Syracusans elect one Dionysius, who had begun his working life as a clerk in a public office, as supreme military commander in 406 BCE because of his achievements in the war against Carthage that had begun in 409 BCE.

Hannibal, whose Carthaginian forces return to Sicily, dies during the campaign in a plague that had broken out during the siege of Akragas in 406 BCE, but his brother Himilco forces the city's surrender after eight months, following which the Carthaginian troops plunder and destroy the city.

The destruction of Athens' fleet at Aegospotami effectively ends the Peloponnesian War, and Athens surrenders in the following year.

Sparta has resoundingly failed to destroy the Athenian empire, and in this sense Athens, whatever its financial and human losses, has won the Peloponnesian War.

Thucydides observes that contemporary Greeks were shocked not that Athens eventually fell after the defeat in Sicily, but rather that it fought on for as long as it did, so devastating were the losses suffered.

The Corinthian War, pitting Sparta against a coalition of four allied states, Thebes, Athens, Corinth, and Argos, which are initially backed by Persia, lasts from 395 BCE until 387 BCE.

The immediate cause of the war was a local conflict in northwest Greece in which both Thebes and Sparta intervened.

The results are inconclusive: under the Peace of Antalcidas, dictated by Persia, Ionia is ceded to Persia and the Boeotian league is dissolved, as is the union of Argos and Corinth.