When does Achilles leave the war in the iliad?

Achilles leaves the war in Homer's "Iliad" in Book 1, following a dispute with Agamemnon over the taking of his war prize, Briseis. Feeling dishonored and angry at Agamemnon's actions, Achilles withdraws from the battle and refuses to fight for the Greeks any longer. His absence has significant consequences for the Greek forces, leading to a series of defeats against the Trojans. Achilles' withdrawal sets the stage for much of the conflict and drama that unfolds throughout the epic.