After the breakdown of Roman rule in Britain in the 5th century, present day England was progressively settled by Germanic groups collectively known as the Anglo-Saxons. The Jutes and Saxons settled in the south-east of the island, and the Angles in Norfolk, Suffolk, the Midlands and the north. Fragmentary knowledge of Anglo-Saxon England in the 5th and 6th centuries comes from the British writer Gildas (6th century), the Anglo-Saxon Chronicle (a history of the English people begun in the 9th century), saints' lives, poetry, archaeological findings, and place-name studies. Around 495, at the Battle of Mount Badon, Britons inflicted a severe defeat on the Anglo-Saxons which halted their westward advance for some decades. However, Anglo-Saxon expansion resumed in the sixth century. From about 500 AD, the Anglo-Saxon areas of England were divided into seven petty kingdoms, known as the Heptarchy: Northumbria, Mercia, East Anglia, Essex, Kent, Sussex, and Wessex. The kingdoms tended to coalesce and expand into the areas retained by the Britons by means of warfare. The West Saxon victory at the Battle of Deorham in 577 brought the Anglo-Saxons to the Bristol Channel and separated the Britons in Wales from those in Dumnonia and Cornubia; the Northumbrian victory at Chester around 616 separated Wales from the Britons of Cumbria. Gradual Anglo-Saxon expansion over the next 300 years forced the Britons to retreat, as the dominant culture, to the approximate borders of modern Wales in the west, the River Tamar in the south west and the River Forth in the north. The dominant themes of the seventh to tenth centuries were the spread of Christianity and the political unification of England. Christianity is thought to have come from three directions — from Rome to the south, and Scotland and Ireland to the north and west. The first recorded Viking attack in Britain was in 793 at Lindisfarne monastery. The conquest of Northumbria, north-western Mercia and East Anglia by the Danes led to widespread Danish settlement in these areas. However, Alfred the Great's victory at Edington in 878 stemmed Danish attacks. By the end of his reign in 899 he was the only remaining English king, having reduced Mercia and Cornwall to dependencies of Wessex. Alfred's grandson Athelstan became the first king to achieve direct rulership of what we would now consider England in 927, although unification did not become permanent until 954, when Edred defeated Eric Bloodaxe and became King of England.
In 1016, the Viking king Cnut the Great became ruler of England, as part of a short-lived empire which also included Denmark and Norway. However, with the accession of Edward the Confessor, heir of the native English dynasty, in 1042, England once again became a sovereign kingdom. Its ties and nature, however, were forever changed following the Norman conquest of England in 1066. The next few hundred years saw England as a major part of expanding and dwindling empires based in France, with the "Kings of England" using England as a source of troops to enlarge their personal holdings in France for years (Hundred Years' War); in fact the English crown did not relinquish its last foothold on mainland France until Calais was lost, in 1558, during the reign of Mary Tudor (the Channel Islands are still crown dependencies, though not part of the UK). In the 13th century Wales (the remaining Romano-Celts) was brought under the control of English monarchs through conquest. This was formalised in the Statute of Rhuddlan in 1284 and Wales was legally annexed to the Kingdom of England by the Laws in Wales Acts 1535–1542. Wales shared a legal identity with England as the joint entity originally called England and later England and Wales. An epidemic of catastrophic proportions, the Black Death first reached England in the summer of 1348. The Black Death is estimated to have killed between a third and two-thirds of Europe's population. England alone lost as much as 70% of its population, which passed from seven million to two million in 1400. The plague repeatedly returned to haunt England throughout the 14th to 17th centuries. The Great Plague of London in 1665–1666 was the last plague outbreak.