The ruling Molossian Aeacidae dynasty managed to create the first centralized state in Epirus c. 370 BC, expanding their power at the expense of rival tribes. The Aeacids allied themselves with the increasingly powerful kingdom of Macedon, in part against the common threat of Illyrian raids, and in 359 BC the Molossian princess Olympias, niece of Arybbas of Epirus, married King Philip II of Macedon (r. 359–336 BC). She was to become the mother of Alexander the Great. On the death of Arybbas, Alexander the Molossian, uncle of Alexander the Great of Macedon, succeeded to the throne with the title "King of Epirus".