This chapter deals with the political history of Assyria from the eleventh to the ninth century bc, from the reign of Tiglath-pileser I (1114–1076 bc) to that of Ashurnasirpal II (883–859 bc). The most striking feature of this period is the temporary decline of Assyria, the territorial extent and political influence of which reached a nadir in the first half of the tenth century bc, and its subsequent revival during the late tenth and early ninth centuries bc. Based on a close examination of the extant textual sources, this chapter focuses on how the system of Assyrian territorial governance established in the late second millennium bc collapsed and how a new system of governance was established, especially during the reign of Ashurnasirpal II. This king also moved the political capital from Assur to Kalhu (modern Nimrud) and took the first, decisive steps toward the creation of an entirely new political entity: the Assyrian Empire.