There are several:
To provide the squabbling Greek city states he had tentatively united with a common enemy to focus on;
To fulfil his dreams and ambitions;
To gain control of the fabled wealth and power of the Persian Emperor;
To get revenge for Greek defeats at the hands of the Persians;
To free Greek cities under Persian control
To provide the squabbling Greek city states he had tentatively united with a common enemy to focus on;
To fulfil his dreams and ambitions;
To gain control of the fabled wealth and power of the Persian Emperor;
To get revenge for Greek defeats at the hands of the Persians;
To free Greek cities under Persian control
