The Senate took advantage of Carthage's difficulties in the Mercenary War to seize Sardinia. Polybius rightly regarded the latter action as unjustified and the subsequent Carthaginian resentment as a major cause of the Second Punic War. The treaty between Hannibal and Philip V of Macedon clearly envisaged Rome's continuing existence after a Carthaginian victory. Hannibal left Carthago Nova sometime in May, and reached the Rhone in September. Scipio, with an army destined for Spain, arrived by sea at the mouth of the Rhone at the same time. Scipio now sent the major part of his forces to Spain under the command of his brother Gnaeus, while he himself returned to Italy. Sicily and Sardinia were the prizes won by Rome as a result of the First Punic War and its aftermath. They were finally organized as provinces in 227 but in Sicily the kingdom of Syracuse, like the city of Messana, remained an independent state, bound to Rome by treaty.

With the decline of Tyre the string of trading posts, which the Phoenicians founded from Gades on the Atlantic shore of Spain round to Malaca, Sexi and Abdera along the south-west Mediterranean coast, gradually passed into Carthaginian hands. A turning-point in Carthaginian relations with the Greeks was the battle of Alalia, where with their Etruscan allies they smashed Phocaean sea-power. When the First Punic War ended Hamilcar Barca remained undefeated in Sicily and was then given full powers by the Carthaginian government to negotiate a peace settlement with Rome. Hamilcar was succeeded in the governorship of Spain by his son-in-law and admiral, Hasdrubal, who was first chosen by the troops. On the death of Hasdrubal the army in Spain enthusiastically conferred the command on Hannibal, and this appointment was quickly confirmed by the Carthaginian government by a unanimous vote. Polybius condemns the Carthaginians in regard to Saguntum, but he equally condemns the Romans for their previous unjust seizure of Sardinia.