The conflict began as a response to the offensive activities undertaken by Hermocrates of Syracuse against Carthaginian territories in Sicily, particularly Selinus, after 408 BC.
In response, Carthage dispatched an army under the command of Hannibal Mago and Himilco II, members of the Magonid family, to Sicily.
Upon reaching Camarina, Dionysius made the controversial decision to order the inhabitants to abandon their city instead of preparing for a defensive stand.
Eventually, a peace treaty was established which affirmed Carthaginian control over Selinus, Akragas, Gela, and Camarina.
This event marked a significant point in the Sicilian Wars, with Carthage attaining peak control over Sicily, a level of dominance that wouldn't be seen again until after the demise of Agathocles in 289 BC.
Carthage had isolated itself from Sicilian affairs for almost 70 years, following the defeat at Himera in 480 BC, during which time Greek culture had started to penetrate the Elymian, Sikanian and Sicel cities in Sicily.
Syracuse and Akragas, the leading Greek cities in Sicily did not confront Carthage at that time and the Carthaginian army withdrew with the spoils of war.
Although Syracuse was involved in the Peloponnesian War and with disputes with her neighbours, their government sent an appeal for support to Magna Graecia and mainland Greece once the Carthaginians landed in Sicily.
While building siege ramps for future attacks the army was struck by plague and Hannibal along with thousands of Carthaginians perished.
Himilco saved the situation by managing to defeat the Syracusan fleet and capturing the grain convoy bound for Akragas.
It is not known if the Carthaginians had received any reinforcement during the winter to make up their losses, but Himilco had left the Punic fleet at Motya, thus becoming dependent of a long supply line.
While the Carthaginians wintered at Akragas, Akragan refugees made accusations against the Syracusan generals after reaching that city.
He got the government to recall political exiles (former followers of Hermocrates like himself – and potential allies), and then marched to Gela with 2,000 foot and 400 horse, which was then under the command of the Spartan Dexippus.
Dionysius then marched to Leontini, held a military assembly, and after some stage-managed theatrics, got the citizens present to give him a bodyguard of 600 men,[9] which he eventually increased to 1,000 mercenaries.
Clumsy coordination between the individual detachments of the Greek army caused a defeat in detail for its divisions instead of achieving a double envelopment of the Carthaginian force.
The heavy infantry fought in close formation, armed with long spears and round shields, wearing helmets and linen cuirasses.
The Libyans, Carthaginian citizens and the Libyo-Phoenicians provided disciplined, well trained cavalry equipped with thrusting spears and round shields.
Numidia provided superb light cavalry armed with bundles of javelins and riding without bridle or saddle.
The mainstay of the Greek army was the Hoplite, drawn mainly from the citizens, but Dionysius had a large number of mercenaries from Italy and Greece as well.
Reasons included: he was outnumbered, the Greek soldiers had refused to continue the harassing tactics he was using against the Carthaginian foragers and supply ships, and getting besieged in Gela during the winter would cut him off from Syracuse, where his political position was secure but not solid, and might lead to his opponents moving to depose him.
[20] The rapid surrender of two Greek cities without a fight was detrimental to the reputation of an aspiring war leader, even if it was based on sound military reasoning and correct political judgement.
The suffering of women, old folk, and children on the road affected the mood of the soldiers escorting the throng, and rumours began to spread on the motives of Dionysius.
The cavalry of Syracuse, made of noblemen and former oligarchs, considered assassinating Dionysius, but he was too well guarded by his mercenaries for them to find an opportunity.
The Carthaginians left Sicily soon after the treaty was signed, while Greeks returned to repopulate Akragas, Camarina and Gela, but these cities never reached their former prominence and never again threatened the position of Syracuse – which would help Dionysius in his wars against Carthage and the Sicels.
Gela and Camarina never recovered, Akragas regained some semblance of her former power but not her status as the wealthiest city in Sicily.
As Carthage took no action, Dionysius increased his power and domain in Sicily and finally in 398 BC launched a war against the Carthaginians by attacking Motya.
Ironically, Carthage had helped keep Dionysius in power by providing him with Campanian mercenaries when the Syracusan rebels had him besieged in Syracuse.