Troy was annihilated by Greek soldiers over the love of Helen of Troy.
Aeneas was one of the scarce Trojan survivors and on the command of the Gods, fled and sailed to Italy.
After all attempts at finding a new home failed, him and the group of exiled Trojans were welcomed by Latinus, king of the Latins.
Latinus' daughter Lavinia was promised to Turnus, the king of the Rituli however Latinus was given a prophecy that Lavinia would be betrothed to one from another land-Aeneas.
Latinus believed in the prophecy and consequently, Turnus, at the urging of Juno, waged war on Aeneas.