Persia

The Persian Empire (also known as the Achaemenid Empire or the First Persian Empire) was the largest empire in the world at the time, stretching from Greece to Libya to India.

It successfully took control of northern Greece but failed in its attempts to conquer all the Greeks, eventually being pushed out of Europe in the Greco-Persian Wars. It aided Sparta in the Peloponnesian War, preferring them to Athens as the dominant power in Greece. It was eventually conquered by Alexander the Great.

Persia followed a monotheistic gnostic religion named Zoroastrianism which worships Ahura Mazda, although it was tolerant of other religions and cultures. It attempted to spread its religion but did not enforce it, generally being benevolent to its subjects. The main exception is Egypt, which was often treated fairly poorly, leading to Alexander being welcomed as a liberator rather than a conqueror when he arrived.