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.