While Cyaxares took to his own share the land of the conquered people, Assyria Proper, and the countries dependent on Assyria towards the north and north-west, Nabopolassar was allowed, not merely Babylonia, Chaldaea, and Susiana, but the valley of the Euphrates and the countries to which that valley conducted.

Thus two considerable empires arose at the same time cut of the ashes of Assyria--the Babylonian towards the south and the south-west, stretching from Luristan to the borders of Egypt, the Median towards the north, reaching from the salt desert of Iran to Amanus and the Upper Euphrates.
These empires were established by mutual consent; they were connected together, not merely by treaties, but by the ties of affinity which united their rulers; and, instead of cherishing, as might have been expected, a mutual suspicion and distrust, they seem to have really entertained the most friendly feelings towards one another, and to have been ready on all emergencies to lend each other important assistance.
For once in the history of the world two powerful monarchies were seen to stand side by side, not only without collision, but without jealousy or rancor.

Babylonia and Media were content to share between them the empire of Western Asia: the world was, they thought, wide enough for both; and so, though they could not but have had in some respects conflicting interests, they remained close friends and allies for more than half a century.
To the Median monarch the conquest of Assyria did not bring a time of repose.

Wandering bands of Scythians were still, it is probable, committing ravages in many parts of Western Asia.

The subjects of Assyria, set free by her downfall, were likely to use the occasion for the assertion of their independence, if they were not immediately shown that a power of at least equal strength had taken her place, and was prepared to claim her inheritance.