Why are the Medes and Persians included in Daniel 2's prophecy?
The Medes and Persians are included because they were the next great Gentile empire after Babylon, and they also held sway over the nation of Israel. Daniel 2's image previewed empires that had a direct relationship with Israel, so Persia's rule over the Jews placed it in the prophecy.
Les explains that the great image in Daniel 2 was a preview of the coming great Gentile empires in ancient times, specifically those empires that had a direct relationship with the nation of Israel. Babylon was the first, and it destroyed Jerusalem and took the Jews captive. While Daniel and Ezekiel were servants of the Babylonian government, the next empire came up: the Medes and the Persians. They held sway for a long period of time, but they were also over the nation of Israel. That is why they are in prophecy.