How is Agamemnon is a violent story of a primitive family feud?

Agamemnon, the first play in Aeschylus' Oresteia trilogy, tells the story of the murder of Agamemnon. Prior to leaving Argos to wage the Trojan War, Agamemnon sacrificed his daughter, Iphigenia, to placate the wrath of Artemis. This infuriated Clytaemnestra, Agamemnon's wife. She spent the next decade plotting her revenge. Upon his return, she murdered Agamemnon, along with Cassandra, his new concubine. The cycle of revenge continued throughout the remaining to plays in the trilogy, as the son of Agamemnon and Clytaemnestra--Orestes--killed his mother and then the furies sought to exact vengeance on Orestes.
Agamemnon and the Oresteia in general represents a primitive family feud because the stakes of the feud--the life and death of its participants--were much higher than those in more contemporary family feuds. Both Clytaemnestra and Orestes took the law into their own hands, and Apollo even commanded Orestes to exact vengeance on his mother.