How the Persian invasion under King Xerces united the Greek city states and
furthered the aims of democracy.

Xerxes I was a great ruler in the ancient world.

Explanation:

Xerxes was the 5th century BC king of the Achaemenid Empire in Persia. Around 486 BCE, Xerxes took the throne and became emperor with a zeal to go for a war with Greece. As the Persian made their way fro Asia Minor to Greece, they began to meet Greek resistance. The Greek city-states were an independent kingdom, but they had formed a rough alliance to fight off the intruders. Xerxes defeated the Spartans at Thermopylae, conquered Attica, and sacked Athens.

To prevent Greece from ending in the hands of enemies after Xerxes I attack, many of the Greek city-states decided to introduce democracy. Athenian democracy introduced around the sixth century BC in the Polis (Athens). By doing this, they were able to unite together and make decisions regarding threats from invaders.

the roman army grew in size and became dominant in the mediterranean region.