The Medes were Indo-Iranian (modern designation, and of course, if memory serves), and were one of the two large groups (the other being the Scythians) which entered the Near East during the final decades of the Assyrian Empire. Nineveh was the capital of Assyria, and for a number of years there was a balance of power, with the Babylonians resisting Assyrian domination and allied with (I think) the Scythians, and the Medes allied with the Assyrians. Somehow or other the Babylonians sweet talked the Medes into changing sides, Nineveh was stormed, and the Assyrian Empire was no more. Well, for all practical purposes. There was one more king of kings, but he got nowhere, and the Assyrians became a regional ethnic minority.
Danke’,
As I recall though, the Assyrians overtook Babylon and captured the city fairly quickly?