 Complete the following phrase:  By the ninth century the many kingdoms of the early Anglo-Saxon period had been consolidated into four: Wessex, Mercia, Northumbria and East Anglia. In the eighth century, Mercia had been the most powerful kingdom in southern England, but in the early ninth, Wessex became domit under Æthelstans great-great-grandfather, Egbert. In the middle of the century, England came under increasing attack from Viking raids, culminating in invasion by the Great Heathen Army in 865. By 878, the Vikings had overrun East Anglia, Northumbria, and Mercia, and nearly conquered Wessex. The West Saxons fought back under Alfred the Great, and achieved a decisive victory at the 