Thyestes killed Atreus. While Thyestes ruled Mycenae, the sons of Atreus, Agamemnon and Menelaus, were exiled to Sparta. There, King Tyndareus accepted them as the royalty that they were. Shortly after, he helped the brothers return to Mycenae to overthrow Thyestes, forcing him to live in Cytheria, where he died. As a token of good will and allegiance, King Tyndareus offered his daughters to Agamemnon and Menelaus as wives, Clytemnestra and Helen respectively. When Agamemnon left Mycenae for the Trojan War, Aegisthus seduced Agamemnon's wife, Clytemnestra, and the couple plotted to kill her husband upon his return. They succeeded, killing Agamemnon
History of Sparta Peace of Callias. Again the Thebans refused to renounce their Boeotian hegemony, and the Spartan's sent a force under King Cleombrotus in an attempt to enforce Theban acceptance. When the Thebans gave battle at Leuctra, it was more out of brave despair than hope. However, it was Sparta that was defeated and this, along with the death of King Cleombrotus dealt a crushing blow to Spartan military prestige. The result of the battle was to transfer supremacy from Sparta to Thebes. As Spartan citizenship was inherited by blood, Sparta now increasingly faced a helot population that vastly outnumbered its citizens.