Final answer:
The Mamertines were mercenaries in control of Messina, and their plea to Rome for aid led to a complicated diplomatic situation that contributed to the start of the First Punic War.
Step-by-step explanation:
The Mamertines were a group of mercenaries who controlled the city of Messina in Sicily. Their request for aid from Rome placed the Romans in an awkward position because it involved Rome in a conflict on Sicily, escalating tensions with Carthage and indirectly leading to the outbreak of the First Punic War.
The Carthaginians, who had initially helped the Mamertines against Syracuse, felt betrayed when the Mamertines sought help from Rome, their rival. This not only triggered a diplomatic crisis but also posed a dilemma for Rome, which, at the time, saw an opportunity to expand its influence in the region despite the risk of war with Carthage.