What are the major themes of Iphigenia in Aulis by Euripides?

Iphigenia in Aulis by Euripides is a sort of prequel to Homer's Iliad. It describes an important event immediately preceding the Trojan War. The ships waiting to leave for Troy are becalmed at Aulis and the oracle, Calchas, explains that Agamemnon must sacrifice his daughter, Iphigenia, to the goddess Artemis to obtain favorable winds. 

The first theme in the play is heroism. Although Agamemnon and Menelaus are, in theory, "heroes" of the Trojan War,...

Iphigenia in Aulis by Euripides is a sort of prequel to Homer's Iliad. It describes an important event immediately preceding the Trojan War. The ships waiting to leave for Troy are becalmed at Aulis and the oracle, Calchas, explains that Agamemnon must sacrifice his daughter, Iphigenia, to the goddess Artemis to obtain favorable winds. 

The first theme in the play is heroism. Although Agamemnon and Menelaus are, in theory, "heroes" of the Trojan War, the true heroism in the play is displayed by Iphigenia, a young girl who is lied to and betrayed by her father, but nonetheless bravely offers to sacrifice herself for the greater good. Achilles, in his offer to defend Iphigenia also displays great nobility of character, but Iphigenia says:

“Death will be my wedding, children and glory.”

The second theme has to do with war. The play was written during the Peloponnesian Wars, which Euripides opposed. The major message of the play is that wars kill the innocent for the sake of the desire for glory and conquest. As Helen went willingly with Paris (with the blessing of the goddess Aphrodite), there was really no justification for the war other than the wounded ego of Menelaus. By showing the very opening of the war as an exercise in unjust slaughter of a innocent young girl, Euripides emphasizes that all wars other than those of self defense are morally unjustifiable. 

The final theme is family and gender. Both the cause of the war and the sacrifice of Iphigenia involve family issues, but with the needs of the patriarchs trumping all other aspects of family life. Thus patriarchy and war are associated in the play.