Why did Agamemnon sacrifice his daughter according to history?

By history I hope you mean mythology, because the Trojan War may have happened, but it certainly did not happen the way Homer describes it. Agamemnon had killed a deer sacred to Artemis while hunting. read more

In Greek mythology, Iphigenia was a daughter of King Agamemnon and Queen Clytemnestra, and thus a princess of Mycenae. Agamemnon offends the goddess Artemis, who retaliates by commanding him to kill Iphigenia as a sacrifice so his ships can sail to Troy. In some versions, Iphigenia is sacrificed at Aulis, but in others, Artemis rescues her. In the version where she is saved, she goes to the Taurians and meets her brother Orestes. read more

Meanwhile, the sacrifice of Iphigenia is a cloud over the marriage of Clytemnestra and Agamemnon and ultimately leads to his murder. The description of Iphigenia's murder undermines the audience's sympathy for Agamemnon. read more