The final cause of the Trojan War was Agamemnon's choice to sacrifice Iphigeneia at Aulis after the goddess Artemis bound the troops there due to a perceived slight. The goddess insisted that the blood of Atreus be spilt, or no Achaian would leave Aulis to fight at Troy. This left Agamemnon to decide which one of his children, three daughters and one son, he would summon to his or her death.
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Causes of the Trojan War: Agamemnon’s Grisly Choice
One might ask the following question in response to this situation: why would Agamemnon sacrifice his eldest daughter, Iphigeneia, in order to save his sister-in-law, Helen of Sparta? The situation, however, is more complex that it at first seems. Agamemnon is not only choosing to save his sister-in-law, but is also choosing to honor his relationship to his brother and to add to his own personal store of honor (timê in Ancient Greek).
The argument which sways Agamemnon, if Herodotus' Histories and Sophocles' Antigone are fifth century BCE authorities on the matter, is that Menelaos is the sole brother of Agamemnon; their father Atreus is dead, and that Agamemnon both has two more daughters besides Iphigeneia, and the capacity to procreate more with Klytaimestra, his wife. His primary responsibility, therefore, was to his brother, not his daughter, though she, and not his brother, was under his protection and tutelage. This stark logic does little to alleviate the human emotion that Iphigeneia’s imploring screams likely caused in Agamemnon as she was led to the slaughter. In Euripides’ Iphigenia at Aulis (406 BCE), he adds insult to injury by suggesting that Iphigenia was lured to Aulis under the pretense of marrying the Achaians’ most eligible bachelor, Achilleus, half-god son of Peleus and Thetis. Finally submitting to her fate after initial protest, though, Euripides’ Iphigenia allows her death to be the death which unleashes the fury of the Achaians on the Trojan city.
To think less sentimentally and more strategically, many former suitors of Helen were among the captains of Agamemnon’s troops. Due to their shared oath to Tyndareus during the courting of Helen, each was oath-bound to defend Helen and her husband with their lives. Had Agamemnon not permitted his daughter to be sacrificed, it is possible that the men trapped at Aulis would still have been oath-bound to fight for Helen at Troy and that Artemis would have stay un-appeased without blood spilled from the House of Atreus. Had Iphigeneia not been sacrificed, therefore, it is very possible that Agamemnon himself may have been chosen as sacrifice. So, Agamemnon plausibly had three major motivations at play in his grisly calculus: to honor his brother, or to add to his own honor, or to save his own life are all possible motivations.
Though this final consideration is not strictly speaking a “cause of the Trojan War,” it is itself a “cause of the plot and action of Homer’s Iliad,” and is itself a mini-recreation of the situation between Menelaos and Paris which started the war. In the first book of Homer's Iliad Agamemnon decides to order Achilleus to give Briseis, his fairly won war trophy and concubine, to Agamemnon. Agamemnon gives this command, because he is required by the god Apollo to return his fairly won war trophy and concubine, Chryseis, back to her Trojan Father, the priest of Apollo, Chryses. It is true that Achilleus, insubordinately, called an assembly of Achaians together, as if he were the chieftain of the troops, and then insisted that not even Agamemnon would lay a hand on the prophet Kalchas if he should give bad news (he does; and he is the same prophet who gave the prophecy requiring that Agamemnon sacrifice his own blood on Aulis!). So, Agamemnon was likely already slightly irritated with the actions of his most powerful but also most overbearing captain. Oh, and they had been fighting together for nine years during which time they had, or rather Achilleus had, sacked 23 cities. So, over time the tensions between the two started to build as did real questions about who was the most valuable and excellent of the Achaians. Agamemnon, fresh with the knowledge that he had to return his concubine Chryseis to her father, Chryses, was understandably annoyed and took it out on the person annoying him most: Achilleus.
But was this decision born of emotion a strategically sound one? Agamemnon will later claim that Zeus literally robbed him of his wits when making that decision (Il.19.135-140). Clearly, he had felt a need or desire to assert his authority in some way over the openly disrespectful Achilleus, but in taking Achilleus’ concubine from him unjustly, Achilleus responds by refusing to take part in the fighting any longer. He also goes a step farther and implores his goddess mother to implore Zeus to deny victory to the Achaians in his absence. His mother, the silver footed Nereid, accomplishes this task, and turns the will of Zeus against the Achaians. And thus begin nineteen long books of fighting and mostly losing for the Achaians, followed by another three of victory and two of lament.
But was this decision born of emotion a strategically sound one? Agamemnon will later claim that Zeus literally robbed him of his wits when making that decision (Il.19.135-140). Clearly, he had felt a need or desire to assert his authority in some way over the openly disrespectful Achilleus, but in taking Achilleus’ concubine from him unjustly, Achilleus responds by refusing to take part in the fighting any longer. He also goes a step farther and implores his goddess mother to implore Zeus to deny victory to the Achaians in his absence. His mother, the silver footed Nereid, accomplishes this task, and turns the will of Zeus against the Achaians. And thus begin nineteen long books of fighting and mostly losing for the Achaians, followed by another three of victory and two of lament.