In alliance with a large Egyptian force, Ashuruballit II's army was able to defend Harran from Babylonian-Median attack for a brief period following the Nineveh destruction; however, when the Egyptian army returned to their homeland in 610 BC, the Babylonians and Medians swept into Harran and plundered it, bringing an end to the Assyrian empire.
While it's clear that he was a member of the Assyrian royal family, and that he was a general of the Assyrian army before declaring himself king, there is some disagreement as to whether or not Ashuruballit II was the brother of Sinsharishkun who ruled the empire from 623 BC to 612 BC. He took his name from Ashuruballit I, the Assyrian king who overthrew Mittanian domination in about 1330 BC, and began the Middle Assyrian empire 1330 BC-1076 BC.