Origin in Ekallatum
Shamshi-Adad was an Amorite born in the middle Euphrates kingdom his father Ilu-kabkabu had built at Ekallatum, a city still not located but certainly near Assur.
Rule of Ekallatum
~1833 - ~1818
Most likely around 1833 he inherited rule from his father Ila-kabkabu. He governed about ten to fifteen years until he had to flee to Babylon when Naram-Sin of Eshnunna conquered Ekallatum.
Exile in Babylonia
~1818 - ~1811
Shamshi-Adad remained exiled in Babylonia, perhaps as a diplomat, until Naram-Sin died seven years later. Upon Naram-Sin's death, Shamshi-Adad returned to Ekallatum.
Road to Ashur
~1811 - ~1808
Upon Naram-Sin's death, Shamshi-Adad took the opportunity to return from exile. Shamshi-Adad I seized the fortress of Ekallatum, thus gaining hegemony east of the Tigris. Just three years later he seized Ashur itself and usurped Erishum I (a son of Naram-Sim) as king of Assyria.
When Shamshi-Adad took Assyria in 1808, he was just the ruler of a minor regional power. He quickly moved to extend Assyrian hegemony from the Euphrates (from whence he came) to the Zagros foothills, and united Ashur, Nineveh and Erbil under a single kingdom. To his southwest was the mighty kingdom of Mari, which was strategically located on the middle Euphrates and was networked with Babylonia and Syria. After clashes with Mari, It became easy prey when its king Yahdun-Lim was assassinated and, likely in 1792, Shamshi-Adad seized the Mari capital itself. Shamshi-Adad took control over the northern Habur Valley, annexing kingdoms such as the land of Apum. Though Ashur remained the formal Assyrian capital, Shamshi-Adad resided at Shehna, which he renamed Shubat-Enlil, for proximity to political currents in Syria. Shamshi-Adad did not just conquer territory, but next installed garrisons and an efficient bureaucracy; simultaneously, he formed inter-dynastic treaties and marriages.
Shamshi-Adad installed his older son Ishme-Dagan as sub-king of Ekallatum, the ancestral home, to govern districts between the Tigris and Zagros; his younger son Yasmah-Adad was sub-king of Mari, and governed districts along the Euphrates, lower Balikh and Habur rivers. Shamshi-Adad directly governed around Shubat-Enlil and placed military governors in charge of cities to its south. A contract drawn up at Sippar in 1782 contained oaths to both Hammurabi and Shamshi-Adad, suggesting his power briefly extended that far south. He was very tolerant of existing practices in the various sates he united. When he took Assur he took on the title "governor of Assur" and in Nineveh he restored the Ishtar temple, said to have been built by Manishtushu five centuries before. Certain cities, such as Qattara, retained their former rulers, who now became his vassals. Local administrative procedures continued to be used, although officials used seals that indicated that they were in the service of Shamshi-Adad.
Yasmah-Adad becomes king of Mari under the auspices of Shamshi-Adad.
Hammurabi inherits the throne of Babylone.
Assyrian Kinglist (Eponym dating system)
Upon taking the throne at Ashur, Shamshi-Adad developed the ZNL5T. It cleverly integrated him into the list of city-rulers by showing a mutual ancestor, the Amorite pre-Assyrian chieftain Apiashal. This legitimized Shamshi-Adad's rule, which disrupted a dynasty. The ZNL5T says he reigned 33 years, allowing us to date his accession to 1808.
One of Shamshi-Adad's lasting legacies was the Assyrian eponym system to date years on documents. Under Shamshi-Adad's rule it became used in such varied places as Mari, Tuttul, Terqa and of course his royal seat at Shubat-Enlil. This Assyrian system of dating thus became the official system for Shamshi-Adad's united upper Mesopotamia.
Despite installing various governors and his sons and sub-kings, Shamshi-Adad kept ultimate authority over his land. This was made clear in the numerous letters to his sons, of which those to Mari were found in a great cache. Those to Yasmah-Adad accused his son of being a lazy weakling. The excerpt below was repeated in his letters.
This micromanagement by great leaders was considered the ideal of kingship at the time. Various other letters chronicle other events, such as when Shamshi-Adad forced Yasmah-Adad to take Beltum (princess of Qatna, a crucial ally against Yamkhad) as his leading wife against his wishes.
How long do we have to guide you in every matter? Are you a child, and not an adult? Don't you have a beard on your chin? When are you going to take charge of your house? Don't you see that your brother is leading vast armies? So, you too, take charge of your palace, your house! Duran, via Van De Mieroop, p 109
Death of Shamshi-Adad I and aftermath
In old age, Shamshi-Adad was attacked simultaneously by Yamkhad and Eshnuna and he died in battle or of natural causes in 1776.
Shamshi-Adad's sons quickly lost control over his territory, though Ishme-Dagan kept hold of Ekallatum and Assur. Land was taken up by existing powers or overtaken by upstarts.
By 1720, due to rainfall changes or popular opposition to court domination, north Mesopotamia had returned to semi-nomadism in villages and the steppe.