A historical anecdote explains why the Macedonians and Spartans never went to war when king Philip conquered all of Greece.

“And then you have Alexander’s cavalry, the companions, which are moving off to the side on one flank. The intent there was hopefully to try and separate the Persian wing opposite Alexander ...

Herodotus claims their Persian opponents numbered 1.7 million ... but when Mardonius himself was killed leading a cavalry charge, the tide changed and most of the force was annihilated.