Pyrrhic War

With the end of the Samnite Wars, Rome had established itself as the lord of central Italy. Conflict with the Greek city-states (Magna Graecia) of southern Italy was unavoidable as its influence grew in the Mediterranean. In the early third century BC, the Lucanians and Bruttians continued to attack these Greek settlements, and in 283 BC, they appealed to the Roman provincial power for assistance. Tarentum was the most powerful city in Magna Graecia at the time.
Its location in southern Italy made it a significant hub for Mediterranean Sea trade while also isolating it from Roman naval action on the Tryrrhenum Sea, which connected Rome to the islands of Corsica and Sardinia. Tarentum had the most formidable naval of any Italian city at the time due to its location and relationship with Greece, and a standing treaty with Rome had been in effect since 302 BC. This contract denied Roman fleets access to the harbour of Tarantum (in Italy's heel), ensuring the Greek navy's autonomy.
In 282 BC, Rome deployed troops by sea to garrison the town of Thurii in response to an appeal for help from regional city-states like as Locri, Rhegim, Croton, and Thurii against the Lucanians. Despite the plea for assistance, Tarentum saw this as a breach of the pact and an act of hostile assault. Tarentum's first response was to drown the Roman fleet and evacuate the garrison from Thurii. In response, the Roman Senate dispatched an embassy to Tarentum under the command of L. Postumius Megellus to demand reparations. During the exchange, the Romans appear to have been insulted (a frequent theme in Livy and Polybius' history to excuse Roman invasion), and Rome declared war. Tarentum, unable to defuse the situation, raised their own army and began fighting.
Pyrrhus, a distant relative of Alexander the Great, imagined himself as a successor to Alexander the Great. He was looking to Italy for growth and glory after just confirming his rule via battle in Epirus. According to Plutarch, the fertile soil of Sicily, rather than Italy, was probably the original goal, but the opportunity to combat the burgeoning might of Rome was too good to pass up. The armies of the post-Alexander Macedonian kingdoms were the most modern and well-equipped of the time, with the Epirotes far ahead of their Roman counterparts. Pyrrhus accepted Tarentum's challenge and sailed across the Adriatic with his own soldiers and those pledged by other regional Greek Kings with the understanding that they would be employed overseas.