Fabius, the Roman annalist, says that besides the outrage on the Saguntines, a cause of the war was Hasdrubal's ambition and love of power.
He tells us how, having acquired a great dominion in <a class="linkToPlace" target="_blank" href="/place?placename=Spain&groupId=983&placeId=1735">Spain</a>, he arrived in <a class="linkToPlace" target="_blank" href="/place?placename=Africa&groupId=300&placeId=294">Africa</a> and attempted to abolish the constitution of <a class="linkToPlace" target="_blank" href="/place?placename=Carthage&groupId=441&placeId=820">Carthage</a> and change the form of government to a monarchy.
The leading statesmen, however, got wind of his project and united to oppose him, upon which Hasdrubal, suspicious of their intentions, left <a class="linkToPlace" target="_blank" href="/place?placename=Africa&groupId=300&placeId=294">Africa</a> and in future governed Iberia as he chose, without paying any attention to the Carthaginian Senate.
Hannibal from boyhood had shared and admired Hasdrubal's principles; and on succeeding to the governor-generalship of Iberia, he had employed the same method as Hasdrubal.
Consequently, he now began this war against <a class="linkToPlace" target="_blank" href="/place?placename=Rome&groupId=935&placeId=1669">Rome</a> on his own initiative and in defiance of Carthaginian opinion,
not a single one of the notables in <a class="linkToPlace" target="_blank" href="/place?placename=Carthage&groupId=441&placeId=820">Carthage</a> approving his conduct towards <a class="linkToPlace" target="_blank" href="/place?placename=Saguntum&groupId=938&placeId=1673">Saguntum</a>.
After telling us this, Fabius says that on the capture of this city the Romans came forward demanding that the Carthaginians should either deliver Hannibal into their hands or accept war.
Now if anyone were to pose the following question to this writer — how opportunity could have better favoured the Carthaginians' wishes or what could have been a juster act and more in their interest (since, as he says, they had disapproved Hannibal's action from the outset)
than to yield to the Roman demand, and by giving up the man who had caused the offence, with some show of reason to destroy by the hands of others the common enemy of their state and secure the safety of their territory, ridding themselves of the war that menaced them and accomplishing their vengeance by a simple resolution —
if anyone, I say, were to ask him this, what would he have to say? Evidently nothing; for so far were they from doing any of the above things that after carrying on the war, in obedience to Hannibal's decision, for seventeen years, they did not abandon the struggle, until finally, every resource on which they relied being now exhausted, their native city and her inhabitants stood in deadly peril.
Walbank Commentary