The Iliad doesn’t tell the Trojan War. It tells a few weeks of it.
Homer’s epic (late 8th or 7th century BC, 24 books, 15,693 lines) covers only part of the tenth and last year: no Trojan Horse, no fall of Troy. Its first word announces the real subject, mēnis, wrath: the wrath of Achilles, from his quarrel with Agamemnon to the death of Hector, and it ends with a funeral and a twelve-day truce, after old Priam goes to Achilles’ tent to beg for his son’s body.
The war around it: Paris of Troy took Helen, wife of Menelaus; Menelaus’ brother Agamemnon led the Greeks; Odysseus was one of their kings. His trip home is the other poem, The Odyssey.
(Troy was real: the ruins at Hisarlik, in today’s Turkey.) Retold from the side by Madeline Miller in The Song of Achilles.
The war itself is a breach of Xenia, the sacred duty of hospitality: Paris was Menelaus’ guest when he left with Helen.