Answer:
Carthage's conquering of Saguntum, which was a Roman ally
Step-by-step explanation:
Rome and Carthage had been in constant war since the First Punic War in the early 3rd Century. And with the victory of the Romans in the sea, Carthage was left with no other choice but to look for any land to capture.
Hannibal, leader of the Carthaginians, led an attack on the town of Saguntum which was an ally of Roma. This event led to the retaliation of Rome to attack Carthage, leading to the Second Punic War.
Thus, the correct answer is the first option.