500
This is why the Chaldeans were able to seize power from the Assyrians around 627 B.C.
What is because the Assyrian empire had been weakened by rebellion; the Assyrian king had died without a male heir, prompting competition for the throne among powerful Assyrians; AND Nabopolassar led the Chaldeans and Medes in a successful revolt against the Assyrians?
(Part III, #14)