In 338, a coalition of Greek city states led by Athens went to war with Alexander's father, Philip, and was decisively defeated at the battle of Chaeronea. Philip was assassinated in 336, and in 335 the city of Thebes, with the backing of Athens, rebelled against Alexander, the new king of Macedonia. Alexander's advisers ( I can imagine a Macedonian version of the Iraq Study Group) suggested that he withdraw from Greece and treat the rebellious tribes on Macedonia's northern borders mildly and by offering them concessions lure them back into allegiance. The Roman historian Plutarch describes Alexander's response:
Alexander was only twenty years old when he inherited his kingdom, which at that moment was beset by formidable jealousies and feuds, and external dangers on every side. The neighbouring barbarian tribes were eager to throw off the Macedonian yoke and longed for the rule of their native kings: as for the Greek states, although Philip had defeated them in battle, he had not had time to subdue them or accustom them to his authority. He had swept away the existing governments, and then, having prepared their peoples for drastic changes, had left them in turmoil and confusion, because he had created a situation which was completely unfamiliar to them. Alexander’s Macedonian advisers feared that a crisis was at hand and urged the young king to leave the Greek states to their own devices and refrain from using any force against them. As for the barbarian tribes, they considered that he should try to win them back to their allegiance by using milder methods, and forestall the first signs of revolt by offering them concessions. Alexander, however, chose precisely the opposite course, and decided that the only way to make his kingdom safe was to act with audacity and a lofty spirit, for he was certain that if he were seen to yield even a fraction of his authority, all his enemies would attack him at once. He swiftly crushed the uprisings among the barbarians by advancing with his army as far as the Danube, where he overcame Syrmus, the king of the Triballi, in a great battle.
Then when the news reached him that the Thebans had revolted and were being supported by the Athenians, he immediately marched south through the pass of Thermopylae. ‘Demosthenes’, he said, ‘called me a boy while I was in Illyria and among the Triballi, and a youth when I was marching through Thessaly; I will show him I am a man by the time I reach the walls of Athens.’When he arrived before Thebes, he wished to give the citizens the opportunity to repent of their actions, and so he merely demanded the surrender of their leaders Phoenix and Prothytes, and offered an amnesty to all the rest if they would some over to his side. The Thebans countered by demanding the surrender of [Macedonian generals] Philotas and Antipater and appealing to all who wished to liberate Greece to range themselves on their side, and at this Alexander ordered his troops to prepare for battle. The Thebans, although greatly outnumbered, fought with a superhuman courage and spirit, but when the Macedonian garrison which had been posted in the citadel of the Cadmeia made a sortie and fell upon them from the rear, the greater part of their army was encircled, they were slaughtered where they stood, and the city was stormed, plundered and razed to the ground. Alexander’s principal object in permitting the sack of Thebes was to frighten the rest of the Greeks into submission by making a terrible example. But he also put forward the excuse that he was redressing the wrongs done to his allies, for the Plataeans and Phocians had both complained of the actions of the Thebans against them. As for the population of Thebes, he singled out the priests , a few citizens who had friendly connections with Macedonia, the descendants of the poet Pindar, and those who had opposed the revolt to be spared: all the rest were publicly sold into slavery to the number of twenty thousand. Those who were killed in the battle numbered more than six thousand ....
After this Alexander came to terms with the Athenians, in spite of their open sympathy with the sufferings of the Thebans.