Carthage

[caesar44]

Rome had violated the treaty by siding with them against Carthage in what was to be Carthage's domain according to the treaty. Hannibal didn't let them get away with the violation.

Here are some reasons not to think that the Roman violated the treaty of 241 -
1. The treaty of 241 did not forbade the Romans from concluding alliances with communities South of the Ebro .

2. "About 225 BC, the Romans, disquieted by the growth of Carthaginian power in Spain, concluded an alliance with the Carthaginian general Hasdrubal that guaranteed the independence of Saguntum and required his forces not to cross the Río Ebro." (http://www.barca.fsnet.co.uk/)

3. "This ‘River’ causes a problem to modern historians. If, as thought by the majority of scholars, the river is the Ebro, in northen Iberia [Spain], then Saguntum is a Greek colony allied with Rome, but a hundred miles inside the Carthaginian sphere of influence. If the River was the Jucar, then Saguntum was the southern outpost of the Roman Empire, but within the territory ceded to Rome. This second choice, the Jucar south of Saguntum, makes much more sense, considering the faulty geography of the ancient world." (http://www.ancientroute.com/cities/saguntum.htm)

4. "Earlier, while Hamilcar was still establishing control of Spain, Rome was concerned over Carthaginian resurgence. In the 220’s BC, they established a treaty with Carthage limiting expansion to anything south of the Ebro. Saguntum, a small town in that territory, had entered into an alliance with Rome, giving the Romans a small stronghold in the heart of Carthaginian lands." ( http://www.unrv.com/empire/second-punic-war.php)

So , as I have said - 1. the treaty of 241 did not forbid a roman alliance with saguntum , 2. - Some say that the "river" was not the Ebro and 3. By all reports , the Carthaginians knew that Saguntum is not for them to take . Many scholars suggests that Hannibal knew exactly what he was doing by taking Saguntum , he wanted an excuse for his war .

Edit : Polybius - "This being so, it is an acknowledged fact that the Saguntines, a good many years before the time of Hannibal, placed themselves under the protection of Rome. The surest proof of this, and one accepted by the Carthaginians themselves, is that when a civil disturbance broke out at Saguntum they did not call in the mediation of the Carthaginians, although they were close at hand and already concerning themselves with Spanish matters, but that of the Romans, and with their help set right the affairs of the state. Therefore, if we take the destruction of Saguntum to be the cause of the war we must allow that the Carthaginians were in the wrong in beginning the war, both in view of the treaty of Lutatius, in which it was stipulated that the allies of each should be secure from attack by the other, and in view of the convention made with Hasdrubal, by which the Carthaginians undertook not to cross the Ebro in arms."