At about the time Hannibal's army descended from the Alps into the North Italian plain, an internicine war broke out between two tribes of Cisalpine Gauls, the Taurini (whence the name of modern Turin) and the Insubres. This conflict provided Hannibal with an opportunity to forcibly engage the attentions of the Gauls.
The Taurini who live at the foot of the mountains
quarrelled with the Insubres and showed no confidence in
the Carthagenians, [Hannibal] at first made overtures for their friendship and alliance, but on their rejecting
these he encamped round their chief city and reduced it
in three days. By massacring those who had been opposed
to him he struck such terror into the neighbouring tribes that they all came in at once and submitted to him.
Livy tells much the same story. The diplomatic maneuverings that underlay this affair are obscure, and somewhat puzzling. It would seem as though Hannibal originally made overtures to the Taurini, and only after these were rejected did he attack and storm their chief town. It may be that the Taurini were the stronger of the two tribes, and that Hannibal initially preferred an alliance with them, attacking them only after their equivocal response to his overtures. Alternatively, he might have called on both combatant tribes to set aside their local dispute and join him against the Romans.
Yet another possibility, however, is that Hannibal simply was looking for an opportunity to make an object demonstration of his army's strength, to dispel any impression the Gauls had formed of its haggard condition so soon after the crossing of the Alps. In that case it may simply have been the bad luck of the Taurini that they were slow to respond favorably to his offers. Had they done so, under this proposed assumption, it would have been the Insubres who would have been his first military victims in Italy.
This scenario is purely speculative, ...