What characteristics contribute to the success and ultimate fall of the persian empire?

The Persian state and Western India to the Indus River was created by Cyrus "the great". He proved wisdom and compassion in the defeat and organization of his empire. His son Cambyses, invaded Egypt. Darius added a new province and Western India then dominated Thrace in Europe, He created the world's largest empire to that time, he divided the empire into 20 provinces. The fall began by Persian kings being secluded out there courts, enclosed by luxuries. Kings upturn taxes, loyalty to empire decline.