Medo-Babylonian conquest of the Assyrian Empire

The Neo-Babylonian Empire under Nabonidus (r.  556–539 BC)

Sinsharishkun's rule of Babylon did not last long, as almost immediately in the wake of him coming to the throne, the general Sin-shumu-lishir rebelled.[8] Sin-shumu-lishir was a key figure during Ashur-etil-ilani's reign, putting down several revolts and possibly being the de facto leader of the country. The new king might have endangered his position, therefore he revolted in an attempt to seize power for himself.[9] Sin-shumu-lishir seized some cities in northern Babylonia, including Nippur and Babylon itself and would rule there for three months before being defeated by Sinsharishkun.[8] Nabopolassar, possibly using the political instability caused by the previous revolt and the ongoing interregnum in the south,[8][11] assaulted both Nippur and Babylon.[n 1] and in the aftermath of a failed Assyrian counterattack, Nabopolassar was formally crowned King of Babylon on November 22/23, 626 BC, restoring Babylonia as an independent kingdom.[12]

In 625–623 BC, Sinsharishkun's forces again attempted to defeat Nabopolassar, campaigning in northern Babylonia. The Assyrian campaigns were initially successful, seizing the city of Sippar in 625 BC and repelling Nabopolassar's attempt to reconquer Nippur. Another Assyrian vassal, Elam, also stopped paying tribute to Assyria during this time and several Babylonian cities, such as Der, revolted and joined Nabopolassar. Realizing the threat this posed, Sinsharishkun led a massive counterattack himself which saw the successful recapture of Uruk in 623 BC.[13] Sinsharishkun could possibly have ultimately been victorious but another revolt, led by an Assyrian general, occurred in the empire's western provinces in 622 BC.[13] This general, whose name remains unknown, took advantage of the absence of Sinsharishkun's forces to march on Nineveh, met an army which surrendered without fighting and successfully seized the Assyrian throne. The surrender of the army indicates that the usurper was an Assyrian and possibly even a member of the royal family, or at least a person that would be acceptable as king.[14] Sinsharishkun then abandoned his Babylonian campaign to defeat the usurper, accomplishing the task after roughly a hundred days of civil war; however the absence of the Assyrian army saw the Babylonians conquer the last remaining Assyrian outposts in Babylonia in 622–620 BC.[13] The Babylonian siege of Uruk had begun by October 622 BC, and though control of the ancient city would shift between Assyria and Babylon, it was firmly under Babylonian rule by 620 BC,[15] and Nabopolassar consolidated his rule over the entirety of Babylonia.[16] During the next several years, the Babylonians scored several other victories against the Assyrians and by 616 BC, Nabopolassar's forces had reached as far as the Balikh River. Pharaoh Psamtik I, Assyria's ally, marched his forces to help Sinsharishkun. The Egyptian Pharaoh had over the last few years campaigned in order to establish dominance over the small city-states of the Levant, and it was in his interests that Assyria survived as a buffer state between his own empire and those of the Babylonians and Medes in the east.[16] A joint Egyptian-Assyrian campaign to capture the city of Gablinu was undertaken in October of 616 BC, but ended in defeat, after which the Egyptian allies kept to the west of the Euphrates, only offering limited support.[17] In 616 BC, the Babylonians defeated the Assyrian forces at Arrapha and pushed them back to the Little Zab.[18] Nabopolassar failed to seize Assur, the ceremonial and religious center of Assyria, in May of the next year, forcing him to retreat to Takrit, but the Assyrians were unable to capture Takrit and end his rebellion.[17]

Map of the Median Empire at its greatest extent (6th century BC), according to the ancient Greek historian Herodotus.

In October or November 615 BC, the Medes under King Cyaxares invaded Assyria and conquered the region around the city of Arrapha in preparation for a great final campaign against the Assyrians.[17] That same year, they defeated Sinsharishkun at the Battle of Tarbisu, and in 614 BC, they conquered Assur, plundering the city and killing many of its inhabitants.[1][18][19][20] Nabopolassar only arrived at Assur after the plunder had already begun and met with Cyaxares, allying with him, signing an anti-Assyrian pact and Nebuchadnezzar, son of Nabopolassar married a Median princess. Shortly after, Sinsharishkun made his last attempt at a counterattack, rushing to rescue the besieged city of Rahilu, but Nabopolassar's army had retreated before a battle could take place.[21] In 612 BC, the Medes and Babylonians joined their forces to besiege Nineveh, taking the city after a lengthy and brutal siege, with the Medes playing a major part in the city's downfall.[21][22][23][24] Although Sinsharishkun's fate is not entirely certain, it is commonly accepted that he died in the defense of Nineveh.[25][26]

After the destruction of Assur in 614 BC, the traditional Assyrian coronation was impossible,[27] so Ashur-uballit II was crowned in Harran, which he made his new capital. While the Babylonians saw him as the Assyrian king, the few remaining subjects Ashur-uballit II governed likely did not share this view, and his formal title remained crown prince (mar šarri, literally meaning "son of the king").[28] However, Ashur-uballit not formally being king does not indicate that his claim to the throne was challenged, only that he had yet to go through with the traditional ceremony.[29] Ashur-uballit's main objective would have been to retake the Assyrian heartland, including Assur and Nineveh. Bolstered by the forces of his allies, Egypt and Mannea, this ambition was quite possible, and his temporary rule from Harran as crown prince, rather than legitimately crowned king, may have seemed more like a temporary circumstance. Instead, Ashur-uballit's rule at Harran composes the final years of the Assyrian state, which at this point, had effectively ceased to exist as an Empire.[2][29][30] After Nabopolassar himself had travelled the recently conquered Assyrian heartland in 610 BC in order to ensure stability, the Medo-Babylonian army embarked on a campaign against Harran in November of 610 BC.[30] Intimidated by the approach of the Medo-Babylonian army, Ashur-uballit and a contingent of Egyptian reinforcements fled the city into the deserts of Syria.[31] The siege of Harran lasted from the winter of 610 BC to the beginning of 609 BC, and the city eventually capitulated.[32] Ashur-uballit's failure at Harran ended the ancient Assyrian monarchy, which would never be restored.[33]

After the Babylonians had ruled Harran for three months, Ashur-uballit, along with a large force of Egyptian soldiers attempted to retake the city, launching a siege in June or July of 609 BC.[31][34] His siege lasted at most two months, until August or September, before being forced to retreat by Nabopolassar; they may have retreated even earlier.[34]