Behind Agamemnon's death is the story of the Trojan War and before that, the bloody legacy of his father. Remember that Aegisthus was Thyestes' only surviving son. His brothers were killed by Agamemnon's father through a scheme that was both barbaric and wickedly creative. Aegisthus, in turn, killed Agamemnon with Clytaemestra's help. Now, Orestes will kill him.
Violence is a cycle that seemingly has no end.
The force of this cycle propels Orestes toward matricide. But that does not mean that matricide is easy or pleasant. When Orestes and Electra call on their father to remember their suffering and the wrongs committed against him, the invocation seems to be as much for them as it is for him. They are working themselves into a frenzy, making themselves bloodthirsty and savage enough to murder their own mother. This frenzy comes with the theme of memory and history.