Why did alexander the great invade persia

This map shows Alexander the Great's massive empire and the route he took to conquer it. When his son, Alexander, took the throne in 336 B.C.E., he vowed to complete the plans of his father. In 334 B.C.E., Alexander invaded Persia, which lay across the Aegean Sea in Asia Minor (modern-day Turkey).

I'm pretty sure it was to get revenge on the Persians for their attack on the Greek people

I think its C) Caste System