Why does the Iliad focus on Achilles’s anger?

The Iliad focuses on the wrath (mēnis) of Achilles because it serves as the primary narrative engine for the poem, driving the catastrophic events that unfold over several weeks near the end of the Trojan War.12

Rather than being a comprehensive history of the war, the poem explores the heroic ideal through the lens of Achilles’s pride and anger, which are triggered when Agamemnon unjustly seizes his war prize, Briseis. This insult leads Achilles to withdraw from battle, allowing his pride to manifest as an excess (hybris) that brings great misfortune to the Achaean army.123

The narrative arc follows the consequences of this anger:
* The Withdrawal: Achilles’s refusal to fight forces the Greeks to suffer under Trojan advances, fulfilling his request to Zeus that the Greeks face grave troubles.12
* The Turning Point: The death of his companion Patroclus shifts Achilles’s focus from personal insult to vengeance.123
* Resolution: The poem concludes by moving beyond this destructive rage, as Achilles is compelled by the gods to restore his magnanimity and civilized values by returning the body of Hector to King Priam.123