26A the rise of medes declining assyrian empire

Between Mesopotamia and the Caspian Sea, tribes of an Indo-European people called Medes had become united under a single king. A later king of the Medes, Cyaxares, reorganized his army and attempted to expand westward against the Assyrians. He allied his army with the Chaldeans, who were now in control of Babylon and Sumer. The Medes and Chaldeans attacked, and together they defeated the Assyrians, overrunning Assyria's capital, Nineveh, in 612. Nineveh's walls were broken by the siege engines that Assyria had introduced centuries before. A community that had existed for more than two thousand years was 

The Medes were an ancient Iranian people[N 2] who lived in Iran in an area known as Media and spoke a northwestern Iranian language referred to as the Median language. Their arrival to the region is associated with the first wave of Iranian tribes in the late second millennium BCE (the Bronze Age collapse) through the beginning of the first millennium BCE.
In the 7th century BCE a unified Median state was formed which together with Babylonia, Lydia, and Egypt became one of the four major powers of the ancient Near East. An alliance with the Babylonians helped the Medes to capture Nineveh in 612 BCE which resulted in the collapse of the Neo-Assyrian Empire. The Medes were subsequently able to establish their Median kingdom (with Ecbatana as their royal centre) beyond their original homeland (central-western Iran) and had eventually a territory stretching roughly from northeastern Iran to the Halys River in Anatolia. The Median kingdom was conquered in 550 BCE by Cyrus the Great who established the next Iranian dynasty - the Achaemenid Empire