Classical Greece was a highly diverse group of city-states loosely bound by shifting political ties and alliances. So it is difficult to generalize about the politics of classical Greece. Around 500 B.C., however, when the two civilizations clashed in war, Athens and Sparta were the most powerful and wealthy of the city-states. After the reforms of Kleisthenes, Athens had become a very limited direct democracy, with members of a governing ekklesia elected from citizens by lot. The government also featured a council of aristocrats, though its powers were becoming limited. Sparta was ruled by two kings, who in practiced answered to a council of elders known as ephors. About 10 percent of the population, known as spartiates, could participate in politics. Both parties worshiped the same pantheon of gods, though Athens in particular was more devoted to the cult of Athena, its legendary founder.
Persia, on the other hand, was ruled by a single monarch (Darius I and his son Xerxes during the wars with the Greeks) who claimed enormous powers. The expansionist nature of the Empire, which stretched from modern Afghanistan to the Levant, meant that power was delegated to satraps, or regional governors who ruled conquered territories. The Persian Empire was both highly centralized in theory but very far-flung and decentralized in practice. They lacked, however, the ideology common among Greek city-states that emphasized individual participation in government. The state religion was a form of Zoroastrianism, though rulers allowed other faiths to exist out of necessity.