Answer:
Phillip II had the dream to build a new Greek empire by winning more land. Alexander invaded and conquered Persia thereby fulfilling his father's dream.
Phillip had an army which mainly consisted of farmers having spears. Phillip II had captured Athens and Thebes which gained momentum and his new army was a combination of Greeks and Macedonians.
Alexander used this army to win eastside lands and took forward the momentum till he completely won over Persia, thus expanding his empire.