*Assyrian Empire 1813-612 BC*
The Assyrians were one of several wealthy and prominent peoples in the Tigris and Euphrates River Valley. They had been present as local states since the third millennium BC, but the formation of Assyria as a kingdom took place in 1813 BC by Shamshi-Adad. The most important cities of their rule were Nimrod, Nineveh, and Ashur.
The Assyrian kings were tributaries of kingdoms such as Kassite, Mitanni, and Babylon for the first few centuries, and after gaining their independence, they were able to unite all of Mesopotamia under one unified kingdom, and even annexed Egypt for a while. The documents discovered from this civilization indicate that the Assyrians were hardworking farmers, diligent merchants, and skilled artists, but more than any other ancient people, they made their living through aggressive military raids, campaigns, and wars, and they often behaved with such cruelty and violence that is almost unparalleled in recorded human history. This method of pride in brutality by their kings and soldiers, who resorted to violence with complete coldness, led to their destruction. 
Although the Assyrians had nationalistic feelings (and this passion and interest eventually led to the creation of a large empire in Mesopotamia), they also loved Sumerian culture very much and were followers of it in every way, adding almost nothing to previous knowledge and simply preserving it. 
Among their most important achievements is the great library of Ashurbanipal, whose purpose was to collect various sciences. This library kept more than a thousand clay tablets and contained information on the knowledge of its time and the administrative and economic levels (one of the largest libraries in history). 
The effective administrative system that this government established to run its empire was very centralized and organized, so that it became a suitable model for later governments. 
The Assyrian government was finally overthrown by the Babylonian government and the Median kingdom in 612 BC.