God announces the impending downfall of the Babylonian empire by comparing its future to the ruins of a previous world power. He declares His intent to step in and bring disaster and strict retribution upon Babylon [מצודת דוד, מצודת ציון]. This punishment directed at the king of Babylon and his land will mirror the exact way God previously punished the king of Assyria [מלבי״ם].
To fully grasp the weight of this comparison, it is helpful to know the historical reality of the time. When this prophecy was given, Assyria was already a completely destroyed and meaningless kingdom. By linking the two empires, the message foresees absolute destruction for Babylon, ensuring it will suffer the exact same fate as Assyria [ביאור שטיינזלץ].