The curse extended to the next generation. In exile Thyestes slept with his own daughter, who gave birth to Aegisthus. Meanwhile, Arteus had two sons, Menelaus and Agamemnon, who married two daughters of Zeus, Helen and Clytemnetra. Agamemnon and Clytamnestra had three children: Iphgenia Electra and Orestes. When the Trojan prince Paris won Helen as a prize and carried her off to Troy. Arteus' sons vowed to win her back, and marshalled their troops to lay siege to Troy. As a gurantee of success, Agamemnon sacrificed his daughter Iphigenia before he set sail.
The introduction of The Oresteia is written Dr. Barbara Belyea. It was a class note for the students in English 237.5 winter session. I hope this introduction will be give you a better understanding of the trilogy: The Oresteia.