Actually i believe Alexander went out and got all the "city states"together under 1 banner, and from there on out started conquering anything around him, backedup by these city-states.
Well, technically the Greek city states were on his side, but alot of that was down to his dad beating the crap out of their armies until they accepted them as their leaders. Upon Philip's death a bunch of them (Athens and Thebes at least) revolted against Macedonian supremacy and had to be suppressed by Alex.
Alex pretty much continued his dad's policy and subjugated the rest of them, put down revolts, etc., then went on to conquer the hell out of more stuff.
So yeah, if they are basing AI behavior on historical AI behavior, then it'd make sense. I don't agree with it, for the record, as he should be using his UA better, but there you go.