30 years of war, Carthage agreed rather than again enter into conflict with Rome. Polybius considered this "contrary to all justice" and modern historians have variously described the Romans' behaviour as "unprovoked aggression and treaty-breaking", "shamelessly opportunistic" and an "unscrupulous act". These events fuelled resentment of Rome in Carthage, which was not reconciled to Rome's perception of its situation. This breach of the recently signed treaty is considered by modern historians to be the single greatest cause of war with Carthage breaking out again in 218BC in the Second Punic War. Carthaginian expansion in Iberia With the suppression of the rebellion, Hamilcar understood that Carthage needed to strengthen its economic and military base if it were to again confront Rome. After the First Punic War, Carthaginian possessions in Iberia (modern Spain and Portugal) were limited to a handful of prosperous coastal cities in the south. Hamilcar took the army which he had led in the Mercenary War to Iberia in 237BC and carved out a quasi-monarchial, autonomous state in its south east. This gave Carthage the silver mines, agricultural wealth, manpower, military facilities such as shipyards, and territorial depth to stand up to future Roman demands with confidence. Hamilcar ruled as a viceroy and was succeeded by his son-in-law, Hasdrubal, in the early 220sBC and then his son, Hannibal, in 221BC. In 226BC the Ebro Treaty was agreed with Rome, specifying the Ebro River as the northern boundary of the Carthaginian sphere of influence. At some time during the next six years Rome made a separate agreement with the city of Saguntum, which was situated well south of the Ebro. Second Punic War, 218–201 BC In 219BC a Carthaginian army under Hannibal besieged, captured and sacked Saguntum and in spring 218BC Rome declared war on Carthage. There were three main military theatres in the war: Italy, where Hannibal defeated the Roman legions repeatedly, with occasional subsidiary campaigns in Sicily, Sardinia and Greece; Iberia, where Hasdrubal, a younger brother of Hannibal, defended the Carthaginian colonial cities with mixed success until moving into Italy; and Africa, where the war was decided. Italy Hannibal crosses the Alps, 218–217 BC In 218BC there was some naval skirmishing in the waters around Sicily; the Romans defeated a Carthaginian attack and captured the island of Malta. In Cisalpine Gaul (modern northern Italy), the major Gallic tribes attacked the Roman colonies there, causing the Roman settlers to