Alexander became king of Macedon at the age of 20.
He succeeded his father, Philip II, in 336 BC after Philip was assassinated at Aigai during a royal wedding. Alexander was proclaimed king immediately by the Macedonian nobles and army. His accession came while he was still a young man, but he had already gained military experience as a commander under his father.
The new king first had to secure his position. Some Greek states and northern peoples challenged Macedonian control, so Alexander campaigned in the Balkans before turning south. In 335 BC, he destroyed Thebes after its revolt, a warning that helped restore Macedonian authority in Greece.
Alexander then inherited Philip’s plan to invade the Persian Empire. He crossed into Asia in 334 BC and spent the rest of his reign campaigning. By the time he died in Babylon in 323 BC, he had created an empire stretching from Greece and Egypt to Central Asia and northwestern India.