By about 1100 BC, Assyria dominated much of north Mesopotamia but over the following 100 or so years pressure from other tribes reduced it to little more than the land on the banks of the River Tigris. From 1000 BC military campaigns were launched to restore Assyrian lands and to gain tribute, booty and resources such as copper and horses. Under Ashurnasirpal II (reigned 883-859 BC) the capital was moved to Kalhu (Nimrud) and the kingdom of Assyria rapidly expanded to the River Euphrates and beyond. The growth of Urartu, a rival kingdom to the north, probably led to a rebellion in Assyria and the accession of Tiglath-Pileser III in 745 BC. From this time onwards defeated countries were ruled directly by Assyria.

Over the following century kings such as Sargon, Sennacherib and Esarhaddon not only built new capitals (Khorsabad and Nineveh) but expanded the empire by conquest until Assyria controlled the region from Iran to the Mediterranean. Under Ashurbanipal (reigned 668-627 BC) problems on the borders in Egypt, Babylonia and Elam were crushed. However, in around 614 BC Nabopolassar, king of Babylon, made an alliance with the Medes from Iran. The combined armies sacked Nineveh in 612 BC and the Assyrian court fled west to the city of Harran where in 609 BC they were defeated by the Babylonians who took over much of the empire.