Compare the political systems of Ancient Greece and the Persian empire, and factors that can explain the differences and similarities?

There are precious few similarities between the political
systems of the two civilizations; in fact they were almost diametrically opposite each
other.

The Persian Empire was ruled by a King from a
central location; however the size of the Empire was such that he could not effectively
rule alone. He employed a number of governors called Satraps to rule in his stead in
various provinces. The Satraps were almost always Persian, but he did allow local
officials to be chosen from local people with local customs and language. To prevent
insurrections or treason, he employed a secret police system known as the "eyes and ears
of the King" who provided him with information of events in the far reaches of his
Empire.

The Greek poleis were each independent of each
other and governed separately. Sparta was most similar to the Persian Empire as it was
ruled by two Kings. The Kings were descended from separate families and did not often
agree with each other. They could and were often overruled by a ruling council known as
the Ephors. Athens was a direct democracy in which all adult male citizens were required
to participate in the government. Some other poleis were ruled by monarchs, others by
the ruling nobility. Others were ruled by politicians or generals who did not gather
power by normal means. They were commonly called "tyrants" because of the method by
which they gained power. In almost every instance, the only commonality between the
Greek poleis was that the spoke a common language and had a great disdain for all thing
foreign. In fact, they often complained that non-Greek persons sounded like the noise of
sheep when they spoke: Baa-baa; hence the term "barbarian.