Alexander’s father, Philip, changed that. In 338 BC he unifies the Greeks into a league that is created basically to fight against the Persians. The Persians at that time were still the dominant world power, and Philip of Macedonia is the figure who unites the Greeks into a league that was able to fight against the Persians. However, he is assassinated, and so, really, it’s young Alexander who now takes over and finds that he has this really powerful military machine. If you can get these Greek city