TL;DR: Rage and war are the topics of Homer’s first great epic poem.
The Iliad (a song about Ilium, or Troy) along with its companion epic the Odyssey form the foundation of ancient Greek culture and address the extremes of human experience through war and peace. Both epics are primary, or oral, epics that draw on an enormous wealth of cultural stories in unified structures that we attribute to the poet Homer, in eighth century B.C.E. The epics are written in an unsentimental style: the Iliad depicts the ambivalence of war in meticulously accurate details. Both the nightmare of war and its excitement find expression in the Iliad, just as the Odyssey’s pages quest for a home, or a peace that seems hard-won after the devastation of war.
The subject of the Iliad is the rage of Achilles and the consequences of that rage for both the Achaeans and the Trojans. War effects not only the men who fight the battles, but also the women and children whose lives are then shaped by its outcome. War represents the worst and, ironically, the best of humanity: ugly brutality and terrible beauty. If you doubt this, look at the place violence holds in our culture; films like The Matrix even show violence as poetic: a graceful dance of destruction that thrills the audience like little else. We both pity with Hector and sympathize with Achilles; neither side of the war holds all of our sentiments. The final outcome of the war, then, becomes truly tragic: only one culture can continue while the other is destroyed or enslaved.
The Iliad's participants are the nobility of both cultures, or the aristoi: "the best people." They are the hereditary holders of wealth and power, and their decisions effect all of the culture. For example, Agamemnon's decision to infuriate Achilles at the outset of the Iliad has lasting effects on the Greek warriors during the last weeks of the Trojan War. Like most epics, of which the Iliad is really the definitive example, the action begins in medias res, a few weeks before the end of a ten-year campaign, with all of the epic's traditional accouterments. The Iliad poses questions, as will the Odyssey, about the nature of political order and what humans must do to maintain that vision and structure. The initial contention in the Iliad is between the Greek champion Achilles and the Greek commander Agamemnon. Who has the stronger claim to right: Agamemnon who has the hereditary position, or Achilles, the one with merit? Ultimately does it matter? When swords are drawn, reason becomes irrelevant.
The Iliad is replete with the culture of men. Indeed, one may argue that all wars since the beginning of time are about men and what they want to control: state, wealth, women. What will men do to maintain their view of order and structure? What are the consequences of the resulting pride, arrogance, destruction? In book one of the Iliad, we discover that because of Agamemnon's refusal to relinquish Chryseis, Apollo has rained a plague upon the Achaean forces. Because he is eventually challenged by Achilles — who represents the wishes of the rest of the men — Agamemnon decides to claim Achilles' prize (a girl named Briseis) to reassert his authority and put Achilles in his place for his challenge. Achilles shows cunning and restraint — qualities that are usually associated with Odysseus — in his argument with Agamemnon, while the latter rages and rails like a wounded child. Yet, when Agamemnon's men take Briseis, Achilles, also child-like, begins to pout by his ships, cries to his mother, and refuses to play the war game anymore. This final decision precipitates the death of many Achaeans, including Achilles’ friend Patroclus. Achilles' resulting rage ends with the death of Hector in book twenty-two, and Achilles' own apocryphal death under the bow of Paris before the war's end.
The brutality of Achilles and its consequences are most evident in Book XXII of the Iliad. Achilles' rage blinds him to anything but the death of Hector, the Trojan champion that killed Patroclus in book sixteen. Replete with epic similes of the hunt, book twenty-two illustrates Hector’s own reluctance to do what he sees as his duty to face Achilles, yet thinks only of himself and what his people might think if he doesn’t face the Greek killing machine (cf. ll. 108-156). Hector’s resolve is soon shaken as he sees Achilles closing, bloody rage the only thing that Achilles sees. Hector flees, but is soon tricked by Athena into stopping to face Achilles, perhaps a commentary on Hector’s need for companionship and Achilles’ desire for only personal vengeance and renown. Hector is mercilessly murdered in front of Troy’s walls, like a fawn at the jaws of a lion.
The death of Hector, then, is given a final cultural context from Hector’s widow Andromache. She now sees the demise of Troy, but personally she sees no future for their son Astyanax. The death of the father, then, is a weighty metaphor for the Trojans: the order that they secured will soon be rendered useless by the barbarity of war; the father’s death leads to the destruction of social order. This theme will be taken up in the Odyssey as well: what is the responsibility of the son for maintaining order in the absence or death of the father? As Andromache sees no future for Astyanax, life does continue even after the carnage of war, yet a new order is imposed on the losers - those who escape death. This theme of continuity is also addressed by Virgil in his Aeneid.
Is war, then, a necessary component of human life? Just because it has been historically up until this point, are we to be like Achilles who could not hear reason through his bloody thoughts: “No truce / till one or the other falls and gluts with blood” (XXII.313–14)? When do we decide that war is better than order?