by @Chris
How a patchwork of Anglo-Saxon kingdoms became one England: the rival powers of Northumbria, Mercia and Wessex, the Great Heathen Army and the Danelaw, the reconquest by Alfred's children and grandson Æthelstan, the Danish kings Sweyn and Cnut, and the Norman conquest up to the fall of Ely. Early medieval frontiers were never surveyed, so borders are drawn soft and follow later shire boundaries; overlordship is shown only where a kingdom was actually absorbed. Sources: Anglo-Saxon Chronicle; Bede, Ecclesiastical History; Wikipedia articles on the kingdoms, the Great Heathen Army, the Danelaw, Æthelflæd, Edward the Elder, Æthelstan, Cnut and the Norman Conquest; borders from Natural Earth admin units.
Picts and Scots → Kingdom of Alba · Northern Britons (Strathclyde, Rheged, Elmet) · Welsh kingdoms · Dumnonia → Cornwall · Northumbria (Bernicia; Bamburgh after 867) · Deira · Mercia · East Anglia · Essex · Kent · Sussex · Wessex → Kingdom of England · Scandinavian York (Jórvík) · Danish Mercia (Five Boroughs) · Danish East Anglia (Guthrum's kingdom) · England under Danish kings (Sweyn, Cnut and sons) · Norman control · The Great Heathen Army · Harald Hardrada's Norwegians · Harold Godwinson's army · William of Normandy's army