How does the greek's history with the persians us understand alexander's "greatness? "?

Persians were constantly attacking Greece and were extremely rich and capable of conquering others. Greece was for them just another small country which they could conquer. No one could dream that Greece could conquer Persia, the best that they could do was defend for a while until the Persians gave up. Alexander is the one who managed to unite all Greece and conquer Persia completely which was unbelievable for the time.

The answer is the Treaty of Portsmouth