Philip II came to power when his older brother Perdiccas III of Macedon () was defeated and killed in battle by the forces of Bardylis. With the use of skillful diplomacy, Philip II was able to make peace with the Illyrians, Thracians, Paeonians, and Athenians who threatened his borders. This allowed him time to dramatically reform the Ancient Macedonian army, establishing the Macedonian phalanx that would prove crucial to his kingdom's success in subduing Greece, with the exception of Sparta. He gradually enhanced his political power by forming marriage alliances with foreign powers, destroying the Chalcidian League in the Olynthian War (349–348 BC), and becoming an elected member of the Thessalian and Amphictyonic Leagues for his role in defeating Phocis in the Third Sacred War (356–346 BC). After the Macedonian victory over a coalition led by Athens and Thebes at the 338 BC Battle of Chaeronea, Philip established the League of Corinth and was elected as its hegemon in anticipation of commanding a united Greek invasion of the Achaemenid Empire under Macedonian hegemony. However, when Philip II was assassinated by one of his bodyguards, he was succeeded by his son Alexander III, better known as Alexander the Great (), who invaded Achaemenid Egypt and Asia and toppled the rule of Darius III, who was forced to flee into Bactria (in what is now Afghanistan) where he was killed by one of his kinsmen, Bessus. This pretender to the throne was eventually executed by Alexander, yet the latter eventually succumbed to an unknown illness at the age of 32, whose death led to the Partition of Babylon by his former generals, the "diadochi", chief among them being Antipater, regent of Alexander IV of Macedon (). This event ushered in the Hellenistic period in West Asia and the Mediterranean world, leading to the formation of the Ptolemaic, Seleucid, and Attalid successor kingdoms in the former territories of Alexander's empire.