Quote Originally Posted by Bootsiuv
It was a feigned retreat.

"On to Makedonia" cried the Athenians as they saw the Mak line collapse and began to surge forward. The more disciplined Thebans who made up the right flank maintained their position.

As the Athenians surged forward, and the Thebans held their ground (as the Athenians should have done), a gap opened up between the two.

Alexander saw this gap, and immediately ordered the companions to strike hard and fast, engulfing the Athenians.

It was at this time that the Makedonians stopped retreating, and began moving forward again. The athenians were crushed, hammer and anvil style.

Alexander was but a young man at this time, but his uncanny ability to detect weaknesses in the enemy battle line was already obvious.
Wasn't that a tactic he and his father Phillip II had decided to do before the battle? That the idea of the feigned retreat was just that, to let the Athenians surge forward and thus open a gap. Or maybe I'm remembering wrong.

And yes, no Greek city state managed to unify all of Greece, because they in most cases lacked the military muscle to do so. One reason for Sparta's loss of hegemony was because they could hardly spare Spartans for garrison duty elsewhere (and thus have a military presence should anyone defy them) as they needed soldiers in Sparta itself should the helots get crazy ideas like fighting for freedom. And if a city state ever got a good position it didn't take long until it's allies became fearful of their own interests and switched sides.
In a Greek city state the military was made up of the middle-class and citizens, so while it did produce reliable troops it meant there would be never be enough of them and mercenaries were a drain on the treasury, a treasury the citizens of a polis would rather see spent on their own city like festivities, temples and public works, even though most of that was financed by the elite. Makedonia did not have the same problem, as the the well-to do Makedonians served in the cavalry and the peasants and hillmen were drafted into the pikemen, although you had exceptions like the hypaspistai.

That is at least my interpretation.