Use the passage to answer the question.
In about 490 B.C., the ancient Persians attempted to expand their empire to include Greece. This period was known as the Persian Wars. Though they were greatly outnumbered, the Greeks defeated the Persians.
Themistocles was able to persuade the Athenians to build a whole fleet of battleships called triremes. Triremes were built with a bronze ram mounted on the front that was used to ram enemy ships below the waterline, causing them to sink. The new ships were powered by three rows of oarsmen on each side who together could reach speeds of about five miles an hour, a very good speed for a battle ship. The trireme became a major asset to the Athenians, allowing them to gain control by sea of much of the land around the Mediterranean and the Black Seas.
According to the passage, what was the cause of the Persian Wars in Ancient Greece? What caused the Greeks to be able to defeat the Persians?