The war is fought between the Trojans (and several native tribes that side with them) and Turnus. Turnus sends a messenger to Diomedes, a king who had founded a large city, to ask for his aid. Diomedes refuses to help Turnus, explaining that he doesn’t want to endanger his people in a war; they’ve seen too much hardship already.
While the Trojan War was the result of a personal offense, Aeneas’s war with Turnus is about the practical matter of staking land. However, Diomedes’s wariness is a reminder that war is never a simple matter; it creates lasting damage far and wide.
Diomedes tells the messenger of his army’s tragedies after they won the Trojan War: when Troy was burning, Ajax had seized a girl from Pallas Athena’s shrine and raped her. This angered the gods, who wrecked their fleet of ships in a violent storm when they tried to sail home. Diomedes was saved from the waves by Athena, but he was forced to abandon his homeland of Argos by Venus, who had held a grudge against him since the Trojan War.
Diomedes’s story shows that the gods’ personal stakes in the Trojan War prolonged the hardships that they faced following the war. Every god in turn was offended by certain actions or took particular likings to war heroes and responded according to these preferences. As a result, many people suffered arbitrary or unfair blessings and curses.
Diomedes’s companions were low-spirited after these events. One of them, Acmon, encouraged them to scorn Venus and said there was nothing she could do to harm them anymore. This angered Venus, so she turned Acmon into a bird. Then, she transformed those who had agreed with Acmon into the same kind of birds. Diomedes explains that, because of these events, he can’t risk the few citizens he has left in the war against Aeneas.
Acmon’s fate is a reminder that no human being can ever get out from under the gods’ power. It is also a reminder that one of the things that most offends the gods is a person’s arrogant refusal to worship them. Venus transforms Acmon into a bird as a result of his confidence, showing that, no matter what, the gods always win with their sheer power.