About 20 years after this rebellion, the Chaldeans regrouped and gained control of the whole Babylonian plain. They established a dynasty that became the most powerful in all of Babylonian history. The famous leader of the Chaldean dynasty was Nabopolassar (625-605 BC). He defeated the Assyrians and was crowned king of Babylon. He brought in the Medes as allies and came to conquer Assyrian territory. He pushed through one city after another until finally he conquered the capital, Nineveh, after a three-month siege in 612 BC.

The Assyrians would not give up easily and the dynasty which was in the West at Harran merged with Egypt to fight against Nabopolassar's armies. In 605 BC it was actually Nabopolassar's son, Nebuchadnezzar II who defeated them at Carchemish when he received word that his father had died thus Babylonia won not only the battle but also the Assyrian Empire.