The Neo-Assyrian Empire reached the height of its extent and power under the Sargonid dynasty, founded by Sargon II. Under Sargon II and his son Sennacherib, the empire was further expanded and the gains were consolidated.
Both kings founded new capitals; Sargon II moved the capital to the new city of Dur-Sharrukin, and the year after, Sennacherib transferred the capital to Nineveh, which he ambitiously expanded and renovated. The conquest of Egypt under Esarhaddon brought Assyria to its greatest-ever extent.
After the death of Ashurbanipal, the Neo-Assyrian Empire swiftly collapsed. One of the primary reasons was the inability of the Neo-Assyrian kings to resolve the “Babylonian problem”; despite many attempts to appease Babylonia in the south, revolts were frequent all throughout the Sargonid period.
The revolt of Babylon under Nabopolassar, in combination with an invasion by the Medes under Cyaxares, led to the Medo-Babylonian conquest of the Assyrian Empire. Assur was sacked and Nineveh fell. The last Assyrian ruler, Ashur-uballit II, tried to rally the Assyrian army at Harran in the west but he was defeated, marking the end of the ancient line of Assyrian kings and of Assyria as a state.