Sîn-šar-iškun ( or , meaning "Sîn has established the king") was the penultimate king of the Neo-Assyrian Empire, reigning from the death of his brother and predecessor Aššur-etil-ilāni in 627 BCE to his own death at the Fall of Nineveh in 612 BCE.
Succeeding his brother in uncertain, possibly violent circumstances, Sîn-šar-iškun was immediately faced by the revolt of one of his brother's chief generals, Sîn-šumu-līšir, who attempted to usurp the throne for himself and briefly took over much of Babylonia. Though Sîn-šumu-līšir was defeated relatively quickly, the instability caused by his revolt, combined with an ongoing interregnum in Babylonia in the south (neither Sîn-šar-iškun nor Sîn-šumu-līšir had formally proclaimed themselves as kings of Babylon) might be what made it possible for Nabopolassar, a southerner of unclear origin, to rise up and seize power in Babylonia. Sîn-šar-iškun's inability to defeat Nabopolassar, despite repeated attempts over the course of several years, allowed Nabopolassar to consolidate power and form the Neo-Babylonian Empire, restoring Babylonian independence after more than a century of Assyrian rule and centuries of domination prior to that.
The Neo-Babylonian Empire, and the Median ruler Cyaxares, technically still a vassal of Assyria, then invaded the Assyrian heartland. In 614 BCE, the Medes captured and sacked Assur, the ceremonial and religious heart of the Assyrian Empire while much of the Assyrian army was occupied fighting the Babylonians, and in 612 BCE their combined armies attacked, brutally sacked, and razed Nineveh, the Assyrian capital. Sîn-šar-iškun's fate is unknown, but it is assumed that he died in the defence of his capital. He was succeeded as king only by Aššur-uballiṭ II, possibly his son, who fought his way out of Nineveh and rallied what remained of the Assyrian army at the city of Harran
Despite the catastrophic fall of Assyria during his time as king, there is nothing to suggest that Sîn-šar-iškun was any less competent than his successful warrior-king predecessors who had dominated Western Asia for centuries. He employed the same tactics as his predecessors and appears to have utilized his forces rationally and strategically, fighting entirely in-line with traditional Assyrian warfare. What doomed the Assyrian Empire might instead have been a combination of the weakening of Assyrian military power caused by internal revolts, the lack of an effective defensive plan for the Assyrian heartland, which had not been successfully invaded in over eight hundred years, over expansion of the Assyrian empire leading its military to be spread too thinly, combined with having to face multiple enemies in large numbers which aimed to outright destroy Assyria rather than simply conquer it.
Background
Chronology As a consequence of Assyria's violent downfall, the period from a few years before the death of Ashurbanipal to the Fall of Nineveh in 612 BCE suffers from a distinct lack of surviving sources. The annals of Ashurbanipal, the primary sources for his reign, go no further than 636 BCE. Although Ashurbanipal's final year is often repeated as 627 BCE, this follows an inscription at Harran made by the mother of the Neo-Babylonian king Nabonidus nearly a century later. The final contemporary evidence for Ashurbanipal being alive and reigning as king is a contract from the city of Nippur made in 631 BCE. To get the attested lengths of the reigns of his successors to match, most scholars agree that Ashurbanipal either died, abdicated or was deposed in 631 BCE. Of the three options, a death in 631 BCE is the most accepted. If Ashurbanipal's reign would have ended in 627 BCE, the inscriptions of his successors Aššur-etil-ilāni and Sîn-šar-iškun in Babylon, covering several years, would have been impossible since the city was seized by the Neo-Babylonian king Nabopolassar in 626 BCE to never again fall into Assyrian hands.
Ashurbanipal had named his successor as early as 660 BCE, when documents referencing a crown prince (probably Aššur-etil-ilāni) were written. He had been the father of at least one son, and probably two, early on in his reign. These early sons were likely Aššur-etil-ilāni and Sîn-šar-iškun. Aššur-etil-ilāni succeeded Ashurbanipal as king in 631 BCE and ruled until his own death in 627 BCE. It is frequently assumed, without any supporting evidence, that Sîn-šar-iškun fought with Aššur-etil-ilāni for the throne.
Sîn-šar-iškun has sometimes historically and erroneously been known as Esarhaddon II after a letter written by Šērūʾa-ēṭirat, a daughter of Sîn-šar-iškun's grandfather Esarhaddon. The chronology and relations of the royal family were uncertain and Šērūʾa-ēṭirat was believed to have been too young to refer to the famous Esarhaddon. The idea of a separate Esarhaddon II as king has been abandoned by Assyriologists since the late 19th century, but the name sometimes appears as a synonym of Sîn-šar-iškun.
Assyria and Babylonia In the middle of the seventh century BCE, the Neo-Assyrian Empire ruled the entire Near East. Due to their powerful standing army and their sophisticated administration, the Assyrians had managed to create the best organized and largest empire that the world had yet seen. Though Babylonia in the south had also once been a large kingdom, it had typically been weaker than its northern neighbor due to internal divisions and the lack of a well-organized army. The population of Babylonia was divided into various ethnic groups with different priorities and ideals. Though old native Babylonians ruled most of the cities, such as Kish, Ur, Uruk, Borsippa, Nippur, and Babylon itself, the Chaldean tribes, led by chieftains who often squabbled with each other, dominated most of the southernmost land. The Arameans lived on the fringes of settled land and were notorious for plundering surrounding territories. Because of the infighting of these three major groups, Babylonia often represented an appealing target for Assyrian campaigns. The two kingdoms had competed since the rise of the Middle Assyrian Empire in the 14th century BCE, and in the 8th century BCE, the Assyrians consistently gained the upper hand. Babylon's internal and external weakness led to its conquest by the Assyrian king Tiglath-Pileser III in 729 BCE.
During the expansion of Assyria into a major empire, the Assyrians had conquered various neighboring kingdoms, either annexing them as Assyrian provinces or turning them into vassal states. Because the Assyrians venerated the long history and culture of Babylon, it was preserved as a full kingdom, either ruled by an appointed client king, or by the Assyrian king in a personal union. The relationship between Assyria and Babylonia was similar to the relationship between Greece and Rome in later centuries; much of Assyria's culture, texts and traditions had been imported from the south. Assyria and Babylonia also shared the same language (Akkadian). The relationship between Assyria and Babylon was emotional in a sense; Neo-Assyrian inscriptions implicitly gender the two countries, calling Assyria the metaphorical "husband" and Babylon its "wife". In the words of the Assyriologist Eckart Frahm, "the Assyrians were in love with Babylon, but also wished to dominate her". Though Babylon was respected as the well-spring of civilization, it was expected to remain passive in political matters, something that Assyria's "Babylonian bride" repeatedly refused to be.
The Assyrians attempted various strategies to appease their Babylonian subjects throughout the eighth and seventh centuries BC; ranging from violent subjugation through war to direct rule either by the Assyrian king or by a representative (sometimes a relative such as a son or brother). Though there was some success in pacifying the urban population of Babylonians, the Arameans and Chaldeans remained unconvinced and repeatedly rebelled whenever they saw an opportunity. Despite the enormous effort spent in keeping the region, Babylonia was seen as too important economically and strategically to allow to secede, but no matter what the Assyrians attempted, rebellion and civil war was the inevitable result each time. Prolonged Assyrian control of Babylonia proved so impossible that modern researchers have dubbed it the "Babylonian problem".
Reign
Rise to the throne and revolt of Sîn-šumu-līšir
In the middle of 627 BCE, Ashurbanipal's son and successor Aššur-etil-ilāni died, leading to Aššur-etil-ilāni's brother Sîn-šar-iškun ascending to the Assyrian throne. Although it has been suggested by several historians, there is no evidence to prove the idea that Aššur-etil-ilāni was deposed in a coup by his brother. Sîn-šar-iškun's inscriptions state that he was selected for the kingship from among several of "his equals" (i.e., his brothers) by the gods.
Also dying at roughly the same time as Aššur-etil-ilāni was the vassal king of Babylon, Kandalanu, which led to Sîn-šar-iškun also becoming the ruler of Babylon, as proven by inscriptions by him in southern cities such as Nippur, Uruk, Sippar and Babylon itself. Sîn-šar-iškun's rule of Babylon did not last long, and almost immediately in the wake of him coming to the throne, the general Sîn-šumu-līšir rebelled. Sîn-šumu-līšir had been a key figure in Assyria during Aššur-etil-ilāni's reign, putting down several revolts and possibly being the leader of the country. The rise of another king might have endangered his position and as such led him to revolt and attempt to seize power for himself. Sîn-šumu-līšir was a eunuch and the only eunuch to claim the throne of Assyria. The possibility that a eunuch, normally trusted due to their perceived lack of political ambition, would do so had never been entertained prior to Sîn-šumu-līšir's attempt.
Sîn-šumu-līšir successfully seized control of some cities in northern Babylonia, including Nippur and Babylon itself and would rule there for three months before Sîn-šar-iškun defeated him. Though both of them exercised control there, it is unclear if Sîn-šar-iškun and Sîn-šumu-līšir actually claimed the title "king of Babylon" (or only used "king of Assyria"), meaning that Babylonia could have experienced an interregnum of sorts. Modern historians typically include both Sîn-šumu-līšir and Sîn-šar-iškun in lists of Babylonian kings, as did some ancient Babylonian king lists.
Rise of Babylon under Nabopolassar
Some months after Sîn-šumu-līšir's revolt, another revolt began in Babylon. An official or general called Nabopolassar, possibly using the political instability caused by the previous revolt and the ongoing interregnum in the south, assaulted both Nippur and Babylon. Nabopolassar's armies took the cities from the garrisons left there by Sîn-šar-iškun but the Assyrian response was swift and in October of 626 BCE, the Assyrian army recaptured Nippur and besieged Nabopolassar at Uruk. A simultaneous Assyrian attempt at recapturing Babylon itself, the last Assyrian action against the city, was repulsed by Nabopolassar's garrison and the attack at Uruk also failed.
In the aftermath of the failed Assyrian counterattack, Nabopolassar was formally crowned king of Babylon on November 22/23 626 BCE, restoring Babylonia as an independent kingdom. In 625–623 BCE, Sîn-šar-iškun's forces again attempted to defeat Nabopolassar, campaigning in northern Babylonia. Initially, these campaigns were successful; in 625 BCE the Assyrians took the city of Sippar and Nabopolassar's attempted reconquest of Nippur failed. Another of Assyria's vassals, 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, Sîn-šar-iškun led a massive counterattack himself which saw the successful recapture of Uruk in 623 BCE.