Persia was really where the power was, but as we get to the mid or the end of the fourth century BCE, Persia weakens, Greece unifies under Philip of Macedon and Alexander the Great and Alexander the Great is able to conquer the Persian Empire and he is short-lived. We have videos on Alexander the Great. I encourage you to watch them. His life is short-lived and his unified empire is short-lived but he has this dream of mixing the cultures and really being a unified people, but as soon as he dies, his empire splits, but the Persian Empire, for the most part, is in the control of the Seleucids and the Seleucid dynasty, this is essentially foreign rule because Seleucus, who establishes the Seleucid dynasty, he is one of Alexander's generals. He's fundamentally Greek and so the rulers under the Seleucid dynasty are Greek and you don't get back to having Persian rule until 238 BCE and it's in 238 BCE that the Parthians emerge to conquer the empire and so once again, you could say, well, this is back to non-foreign rule and it's really important to keep in mind because in its day, the Achaemenid Empire was, if not the dominant, one of the very dominant empires of the world. At its peak, it had a population and this is roughly under Darius the Great and we'll talk more about him. He was an interesting character but the Achaemenid Empire at its peak had approximately 50 million people and that's a lot of people at any time in history but especially at that time in history because at that time in history, there was only a little over 100 million people in the world or at least that's our current estimates so this is actually the largest proportion of the world's population that any empire has ever had in history as far as we can tell so that gives it some claim to being maybe the greatest or one of the greatest empires in world history and then as we get into the Seleucid and especially the Parthian Empire, in the West, we talk a lot about the glory of the Roman Empire but the Parthians were right there beside of them and they kind of went back and forth but they were side by side.