paragraph: At age 16, Alexander's education under Aristotle ended. Philip waged war against Byzantion, leaving Alexander in charge as regent and heir apparent. During Philip's absence, the Thracian Maedi revolted against Macedonia. Alexander responded quickly, driving them from their territory. He colonized it with Greeks, and founded a city named Alexandropolis. Upon Philip's return, he dispatched Alexander with a small force to subdue revolts in southern Thrace. Campaigning against the Greek city of Perinthus, Alexander is reported to have saved his father's life. Meanwhile, the city of Amphissa began to work lands that were sacred to Apollo near Delphi, a sacrilege that gave Philip the opportunity to further intervene in Greek affairs. Still occupied in Thrace, he ordered Alexander to muster an army for a campaign in Greece. Concerned that other Greek states might intervene, Alexander made it look as though he was preparing to attack Illyria instead. During this turmoil, the Illyrians invaded Macedonia, only to be repelled by Alexander. Philip and his army joined his son in 338 BC, and they marched south through Thermopylae, taking it after stubborn resistance from its Theban garrison. They went on to occupy the city of Elatea, only a few days' march from both Athens and Thebes. The Athenians, led by Demosthenes, voted to seek alliance with Thebes against Macedonia. Both Athens and Philip sent embassies to win Thebes' favor, but Athens won the contest. Philip marched on Amphissa (ostensibly acting on the request of the Amphictyonic League), capturing the mercenaries sent there by Demosthenes and accepting the city's surrender. Philip then returned to Elatea, sending a final offer of peace to Athens and Thebes, who both rejected it. 
question: Why did Alexander drive Thracian Maedi from their territory?
answer: Charge as regent