In the previous installments, we saw how the Late Bronze Age balance of power collapsed, and why Urartu — despite its proximity and military competence — could never become a true counterweight to Assyria. In this episode, we turn to a very different kind of rival. If Urartu threatened Assyria from the outside, Babylonia challenged it from within.
Babylonia was not a peripheral power. It was older than Assyria, culturally prestigious, economically vital, and ideologically indispensable. Its kingship carried a legitimacy Assyrian rulers could not simply override. Control of Babylon meant access to southern Mesopotamia’s wealth, but also submission to its religious and political traditions. For that reason, Babylonia would prove to be Assyria’s most formidable rival. Even, and especially, during periods when it was formally ruled by Assyrian kings.
Nabonassar and a moment of parity
The story begins with Nabonassar (r. 747-734 BCE), whose reign overlapped with that of Tiglath-Pileser III (r. 745-727 BCE). Nabonassar inherited a deeply unstable Babylonia, fragmented by powerful Aramaean and Chaldean groups that had eroded royal authority. His primary achievement was internal, restoring a measure of order and reasserting central kingship.
What is striking is how Tiglath-Pileser III responded. He did not invade Babylonia. There is no record of major Assyrian campaigns against Nabonassar. On the contrary, the two rulers appear to have maintained a cooperative relationship. Tiglath-Pileser may even have assisted Nabonassar in subduing Aramaean tribes along their shared frontier, stabilizing the borderlands rather than exploiting Babylonian weakness.
This restraint was deliberate. A stable Babylonia under a legitimate king served Assyrian interests better than chaos in the south. For a brief moment, the relationship between Assyria and Babylonia approached something resembling parity: two strong states acknowledging each other’s interests, neither able to dominate the other without unacceptable cost. It was a fleeting equilibrium and it depended entirely on Nabonassar’s authority.
Intervention without annexation
After Nabonassar’s death, Babylonia again descended into civil war. Competing claimants, tribal leaders, and regional elites struggled for power. This instability posed a strategic dilemma for Assyria. A fragmented Babylonia invited Elamite intervention and offered fertile ground for anti-Assyrian mobilization. Yet outright annexation risked permanent resistance in a land whose traditions Assyria could not easily suppress.
Tiglath-Pileser III chose a carefully calibrated solution. He intervened militarily, restored order, and in 729 BCE assumed the title king of Babylon. Crucially, this was not annexation in the normal Assyrian sense. Babylonia was not reduced to a province. Its institutions, cults, and local administration remained intact. Tiglath-Pileser presented himself as a legitimate Babylonian ruler, participating in traditional rituals and honoring local elites.
This move underscores Babylonia’s unique status. Babylonian kingship was too important to bypass. To rule Babylonia, one had to become a Babylonian king. Yet this solution was inherently unstable. By preserving Babylonian autonomy while asserting Assyrian supremacy, Tiglath-Pileser created a hybrid arrangement that satisfied neither side for long.
Merodach-Baladan II and the counter-hegemony
The fragility of Assyrian control became clear soon after the death of Tiglath-Pileser’s son Salmanassar V (r. 727-722 BCE). Merodach-Baladan II (r. 722-710 BCE), a Chaldean leader from the marshlands, seized power and ruled an independent Babylonia for more than a decade.
Merodach-Baladan understood Babylonia’s strategic value and consciously positioned it as the center of southern resistance to Assyria. He cultivated alliances with Elam, presented himself as the defender of Babylonian tradition, and exploited Assyria’s succession crisis to consolidate power. His success revealed a critical weakness in Assyrian hegemony. Even when Assyria dominated the Near East militarily, it struggled to impose lasting control over Babylonia.
Sargon II (r. 722-705 BCE) eventually expelled Merodach-Baladan in 709 BCE, but the victory was incomplete. The idea of an independent Babylonia — supported by Elam and hostile to Assyria — had proven viable.
Mušezib-Marduk and the cost of domination
Under Sennacherib (r. 705-681 BCE), Babylonian resistance reemerged in an even more destructive form. Mušezib-Marduk (r.693-689 BCE), who had led the anti-Assyrian resistance from the marshes in the south, ruled an independent Babylonia for several years, again with Elamite backing. This phase of conflict was particularly costly. Assyria launched repeated campaigns, while Babylonian elites mobilized local support and foreign allies. The struggle culminated in Sennacherib’s decision to destroy Babylon in 689 BCE, an act without precedent in Assyrian history.
The destruction of Babylon was intended to resolve the Babylonian problem permanently. Instead, it exposed Assyria’s strategic frustration. Babylon could be devastated, but not erased. Its symbolic importance was too great. The outrage provoked by the city’s destruction reverberated throughout Mesopotamia, undermining Assyrian legitimacy rather than strengthening it. Esarhaddon’s subsequent rebuilding of Babylon was an implicit admission of failure. Babylonia could not be ruled through terror alone.
Šamaš-šumu-ukin and the near-fatal experiment
The most dangerous Babylonian challenge came under Ashurbanipal (r. 669-627 BCE). In an effort to stabilize relations with the south, Ashurbanipal attempted something unprecedented: he installed his brother Šamaš-šumu-ukin as king of Babylon, while retaining overall supremacy himself.
The logic was straightforward. By placing a member of the Assyrian royal house on the Babylonian throne, Ashurbanipal hoped to reconcile Babylonian autonomy with imperial control. Babylon would be ruled by a legitimate king who respected its traditions, yet remained bound to Assyria by dynastic loyalty. It was an attempt to institutionalize coexistence rather than enforce domination.
The experiment failed catastrophically. In 652 BCE, Šamaš-šumu-ukin rebelled, mobilizing Babylonian elites, Chaldean groups, Elam, and other disaffected powers in a coordinated uprising. This was a systemic challenge that nearly split the Assyrian Empire in two. For several years, Assyria faced the real prospect of internal collapse, with north and south locked in prolonged war.
Ashurbanipal eventually prevailed in 648 BCE, but the cost was immense. Babylonia was devastated once again, Assyrian resources were severely depleted, and the empire’s ability to respond to new crises was further weakened. Even victory deepened Assyria’s exhaustion.
Nabopolassar and the end of Assyria
By the late seventh century BCE, the pattern was clear. Assyria could suppress Babylonian resistance, but never neutralize it without undermining its own stability. Each intervention drained manpower, wealth, and political capital, leaving the empire increasingly fragile.
When Nabopolassar (r. 626-605 BCE) seized power in Babylonia after the death of Ashurbanipal, Assyria was no longer capable of a decisive response. Weakened by internal strife and succession disputes, it lacked the cohesion that had once allowed it to recover from rebellion. This time, Babylonia did more than regain independence. Allied with the Medes, Nabopolassar turned the tables, dismantling the Assyrian state itself and usurping its empire. Within a generation, Assyria — long the dominant power of the Near East — vanished as a political force.
Babylonia thus proved to be Assyria’s most formidable rival. Not because it always stood outside Assyrian control, but because it never ceased to challenge Assyria from within, until the empire could no longer withstand the strain.
What Babylonia reveals about the failure of balance
Babylonia stands apart from all other Assyrian rivals. It was not marginal. It was not structurally weak. It possessed everything Urartu lacked: demographic depth, economic resources, cultural authority, and strategic centrality. And yet it did not produce balance.
Assyria could not ignore Babylonia, but neither could it resolve the Babylonian problem without undermining its own stability. Control bred resistance, accommodation invited rebellion. Babylonia remained a rival even when ruled by Assyria, perhaps especially then.
If Urartu shows why external challengers failed to balance Assyria, Babylonia shows why internal rivals were even more dangerous. It was the one power that truly threatened Assyria’s survival, and in the end, it was the one that brought the empire down.
In the next installment, we turn eastward to Elam: a state that never sought to replace Assyria, but repeatedly intervened to ensure that Assyria could never feel secure.