During the settlement period the lands ruled by the incomers seem to have been fragmented into numerous tribal territories, but by the 7th century, when substantial evidence of the situation again becomes available, these had coalesced into roughly a dozen kingdoms including Northumbria, Mercia, Wessex, East Anglia, Essex, Kent and Sussex. Over the following centuries, this process of political consolidation continued. The 7th century saw a struggle for hegemony between Northumbria and Mercia, which in the 8th century gave way to Mercian preeminence. In the early 9th century Mercia was displaced as the foremost kingdom by Wessex. Later in that century escalating attacks by the Danes culminated in the conquest of the north and east of England, overthrowing the kingdoms of Northumbria, Mercia and East Anglia. Wessex under Alfred the Great was left as the only surviving English kingdom, and under his successors, it steadily expanded at the expense of the kingdoms of the Danelaw. This brought about the political unification of England, first accomplished under Æthelstan in 927 and definitively established after further conflicts by Eadred in 953. A fresh wave of Scandinavian attacks from the late 10th century ended with the conquest of this united kingdom by Sweyn Forkbeard in 1013 and again by his son Cnut in 1016, turning it into the centre of a short-lived North Sea Empire that also included Denmark and Norway. However, the native royal dynasty was restored with the accession of Edward the Confessor in 1042.