History of Persia
From the Medes and the Persians of 9th Century BC. Of the two main Indo-European tribes moving south into Iran, it is at first the Medes who play the dominant role. With a capital at Ecbatana (modern Hamadan), they establish themselves as powerful neighbours of Assyria. In 612 they combine with Babylon to sack the Assyrian capital at Nineveh. Their spoils are northern Assyria and much of Anatolia, where the Halys river becomes the border between themselves and Lydia. The Medes already control much of Iran including Fars, in the southwest. This is the heartland of the Parsa or Persians, whose king is a vassal of the Medes.