After Cannae, Hannibal needed a maritime base to allow reinforcements and supplies to reach him. But he failed to win over or capture Naples, an old Roman naval ally, and had mixed results elsewhere in Campania: he was successful at proud Capua. He was under-supported from Carthage for all his time in Italy, whether because they could not or would not help him. In 215, he signed a treaty of alliance with Philip V of Macedon. This brought few benefits to either party and would long be remembered by the Romans. Syracuse in Sicily went over to Hannibal in 214 but was recaptured by Claudius Marcellus (late 212). Similarly most of coastal Tarentum in south Italy was in his hands, but only between 212 and 209. In 211, when Capua was under Roman pressure, Hannibal marched on Rome as a diversionary tactic but soon withdrew. Capua fell and was harshly treated.

The crossing of the Rubicon was not the decisive moment it is typically held to be. The Senate had already issued what was in effect a declaration of war, yet Caesar paused after his entry into Italy and initiated discussion of a settlement which even Cicero thought would take effect. Even after Caesar resumed his march it remained unclear until Pompey’s actual embarkation at Brundisium whether there really was a war on.Despite a long scholarly tradition accepting the tendentious claims of Pompey’s side to represent "the Republic," prosopographical analysis shows that the Senate and the Roman nobility who held such authority therein were both deeply divided, while our sources are unanimous that the ordinary citizens of Rome and Italy, including many equites and local officials, were favorable to Caesar, or at least not disposed to cooperate with the Senate's Final Decree. Cicero himself had not tried very hard to join Pompey in his dash to Brundisium, misled (he said) by his belief that a settlement would come about. Even after Pompey's departure from Italy he was far from resolved upon taking his side, not because of innate indecision but the deep ambiguities of the political situation.