"Well, I believe a certain Macedonian started from Persia, did he not? Stopping only when all the known world had fallen?"

That Macedonian was, in fact, a ... (wait for it!)... Macedonian! He conquered Persia before he set out to conquer the rest of the 'known world'. You can hardly blame the ancient Persians for that!

I know there's some tough concepts in there like, 'Macedonians and Persians were different ethnic groups' and 'the conquered are not responsible for the actions of their conquerors' - but keep at it - you'll get there!