This part of the succession plans were not upheld by Ashurbanipal after Esarhaddon's death; Šamaš-šuma-ukin only acceded to the Babylonian throne months after Ashubanipal had become king and was throughout his reign a closely monitored vassal, not entrusted with all of Babylonia or substantial military forces and only allowed to make decisions if they were approved and verified by Ashurbanipal.

Though Šamaš-šuma-ukin maintained peaceful relations with his younger brother for many years, resentment gradually grew between them due to Ashurbanipal's overbearing control.

In 652, Šamaš-šuma-ukin revolted, inspiring the Babylonians to join him and recruiting a coalition of enemies of Assyria, including the Elamites, Chaldeans, Arameans and perhaps the Medes.

Babylon was captured by Ashurbanipal in 648 after a lengthy siege and Šamaš-šuma-ukin died, though the exact circumstances of his death are unclear.

After his defeat and death there is evidence of a large-scale damnatio memoriae campaign, with images of the king being mutilated, erasing his face.

[13] The decision to bypass Šamaš-šuma-ukin as heir to Assyria was also a remarkable one, given that Esarhaddon's own accession issues had been the direct result of his father Sennacherib acting in a similar way.

[7] One hypothesis in regard to why a younger son was designated as the heir to what was clearly Esarhaddon's primary title is that Ashurbanipal and Šamaš-šuma-ukin could have had different mothers.

[15] The decision to grant Šamaš-šuma-ukin Babylonia and designate him and Ashurbanipal as "equal brothers" could perhaps be due to Esarhaddon wishing to avoid the rivalry and jealousy involved in his own accession.

[17] Because Esarhaddon was constantly ill, much of the administrative duties of the empire fell upon Ashurbanipal and Šamaš-šuma-ukin during the last few years of their father's reign.

His coronation was marked by Ashurbanipal returning the religiously important Statue of Marduk, stolen by Sennacherib twenty years prior, to Babylon.

[10] This part of the succession plans were not upheld by Ashurbanipal, who perhaps shifted the balanace of power in his own favor and diminished Šamaš-šuma-ukin's intended status out of fear that his elder brother given a strong power-base would threaten his rule.

[16] Though Ashurbanipal, as king of Assyria, was more powerful, Šamaš-šuma-ukin's kingship of Babylon, important to the Assyrians for military, political, religious and ideological reasons, was prestigious in its own right.

The governors of some Babylonian cities, such as Nippur, Uruk and Ur, and the rulers in the Sea Land, all ignored the existence of a king in Babylon and saw Ashurbanipal as their monarch.

[32] Ashurbanipal had a permanent garrison of troops and officials stationed at Borsippa, a city which would have been deep inside Šamaš-šuma-ukin's domain.

Ashurbanipal identified three groups who aided his brother: first and foremost there were the Chaldeans, Arameans and the other peoples of Babylonia, then there were the Elamites, and lastly the kings of Gutium, Amurru and Meluhha.

This last group of kings might refer to the Medes (as Gutium, Amurru and Meluhha no longer existed at this point) but this is uncertain.

Šamaš-šuma-ukin's ambassadors to the Elamites had offered gifts (called "bribes" by Ashurbanipal) and their king, Ummanigash, sent an army under the command of Undashe, the son of Teumman, to aid in the conflict.

The war quickly turned chaotic; several minor players repeatedly changed sides and both Ashurbanipal and Šamaš-šuma-ukin found it difficult to keep track of their allies.

[45] By 650 Šamaš-šuma-ukin's situation looked grim, with Ashubanipal's forces having besieged Sippar, Borsippa, Kutha and Babylon itself.

[46] Ashurbanipal initiated a bloodbath in the city, described in detail in his later inscriptions: "their carved up bodies I fed to dogs, to pigs, to wolves, to eagles, to birds of the heavens, to fishes of the deep".

As Šamaš-šuma-ukin was both a member of the Assyrian royal family and a traitorous Babylonian king, it was difficult to write of his fate; while scribes eagerly recorded lengthy accounts of the defeat of foreign kings and rebels, there was a general reluctance to write about the death of members of the Assyrian royal family.

Ashurbanipal's inscriptions talk around his brother's death and in many places even omit Šamaš-šuma-ukin's name, simply calling him "the king".

[49] There is evidence of a considerable damnatio memoriae following Šamaš-šuma-ukin's downfall, with steles erected by the king being purposefully mutilated after his death, erasing his face.

He also assumed other traditional Babylonian royal titles, such as šar māt Šumeri u Akkadi ("king of Sumer and Akkad").

[55] Significantly, Šamaš-šuma-ukin left out any mentions of the role of his royal ancestors as chief priests of Assyria's god Ashur, a concept intrinsically linked to Assyrian ideas of kingship.

Despite Šamaš-šuma-ukin publicly identifying himself as an Assyrian (through his genealogy), his inscriptions thus suggest that he did not venerate Assyria's national deity.