Attempts to understand how Roman Britain ends and Anglo-Saxon England begins have been undermined by the division of studies into pre-Roman, Roman and early medieval periods. This groundbreaking new study traces the history of British tribes and British tribal rivalries from the pre-Roman period, through the Roman period and into the post-Roman period. It shows how tribal conflict was central to the arrival of Roman power in Britain and how tribal identities persisted through the Roman period and were a factor in three great convulsions that struck Britain during the Roman centuries. It explores how tribal conflicts may have played a major role in the end of Roman Britain, creating a ‘failed state’ scenario akin in some ways to those seen recently in Bosnia and Iraq, and brought about the arrival of the Anglo-Saxons. Finally, it considers how British tribal territories and British tribal conflicts can be understood as the direct predecessors of the Anglo-Saxon kingdoms and Anglo-Saxon conflicts that form the basis of early English History.