The Roman departure opened the door for the Anglo-Saxon invasion, which is often regarded as the origin of England and the English people. The Anglo-Saxons, a collection of various Germanic peoples, established several kingdoms that became the primary powers in what is now England and parts of southern Scotland.They introduced the Old English language, which displaced the previous British language. The Anglo-Saxons warred with British successor states in Wales, Cornwall, and the Hen Ogledd (Old North; the Brythonic-speaking parts of northern England and southern Scotland), as well as with each other. Raids by the Vikings were frequent after about AD 800, and the Norsemen took control of large parts of what is now England. During this period several rulers attempted to unite the various Anglo-Saxon kingdoms, an effort that led to the emergence of the Kingdom of England by the 10th century.
In 1066, the Normans invaded and conquered England. There was much civil war and battles with other nations throughout the Middle Ages. The Kingdom of England was a sovereign state until the reign of Richard I who made it a vassal of the Holy Roman Empire in 1194. In 1212 during the reign of his brother John Lackland the Kingdom instead became a tribute-paying vassal of the Holy See until the fourteenth century when the Kingdom rejected the overlordship of the Holy See and re-established its sovereignty. During the Renaissance, England was ruled by the Tudors. England had conquered Wales in the 12th century and was then united with Scotland in the early 18th century to form the Kingdom of Great Britain. Following the Industrial Revolution, Great Britain ruled a worldwide Empire, the largest in the world. Following a process of decolonization in the 20th century the vast majority of the empire became independent; however, its cultural impact is widespread and deep in many countries of the present day.
Archaeological evidence indicates that what was later southern Britannia was colonised by humans long before the rest of the British Isles because of its more hospitable climate between and during the various glacial periods of the distant past. The Sweet Track in the Somerset Levels is the oldest timber trackway discovered in Northern Europe and among the oldest roads in the world, and was built in 3807 or 3806 BC.
The first historical mention of the region is from the Massaliote Periplus, a sailing manual for merchants thought to date to the 6th century BC, although cultural and trade links with the continent had existed for millennia prior to this. Pytheas of Massilia wrote of his trading journey to the island around 325 BC.
Later writers such as Pliny the Elder (quoting Timaeus) and Diodorus Siculus (probably drawing on Poseidonius) mention the tin trade from southern Britain, but there is little further historical detail of the people who lived there.
Tacitus wrote that there was no great difference in language between the people of southern Britannia and northern Gaul and noted that the various nations of Britons shared physical characteristics with their continental neighbours
Roman Britain (Britannia)
Julius Caesar invaded southern Britain in 55 and 54 BC and wrote in De Bello Gallico that the population of southern Britannia was extremely large and shared much in common with the Belgae of the Low Countries. Coin evidence and the work of later Roman historians have provided the names of some of the rulers of the disparate tribes and their machinations in what was Britannia. Until the Roman Conquest of Britain, Britain's British population was relatively stable, and by the time of Julius Caesar's first invasion, the British population of what was western old Britain was speaking a Celtic language generally thought to be the forerunner of the modern Brythonic languages. After Julius Caesar abandoned Britain, it fell back into the hands of the Britons and the Belgae.The Romans began their second conquest of Britain in 43 AD, during the reign of Claudius. They annexed the whole of what would become modern England and Wales over the next forty years and periodically extended their control over much of lowland Scotland.
In the wake of the breakdown of Roman rule in Britain around 410, present day England was progressively settled by Germanic groups. Collectively known as the Anglo-Saxons, these included Jutes from Jutland together with larger numbers of Saxons from northwestern Germany and Angles from what is now Schleswig-Holstein. Prior to those settlements some Frisians invaded eastern Britain in the 250s.
They first invaded Britain in the mid 5th century, continuing for several decades. The Jutes appear to have been the principal group of settlers in Kent, the Isle of Wight and parts of coastal Hampshire, while the Saxons predominated in all other areas south of the Thames and in Essex and Middlesex, and the Angles in Norfolk, Suffolk, the Midlands and the north.
The population of Britain dramatically decreased after the Roman period. The reduction seems to have been caused mainly by plague and smallpox. It is known that the plague of Justinian entered the Mediterranean world in the 6th century and first arrived in the British Isles in 544 or 545, when it reached Ireland. The Annales Cambriae mention the death of Maelgwn Wledig, king of Gwynedd from that plague in 547.
 Anglo-Saxon conquests and the founding of England
In approximately 495, at the Battle of Mount Badon, Britons inflicted a severe defeat on an invading Anglo-Saxon army which halted the westward Anglo-Saxon advance for some decades. Archaeological evidence collected from pagan Anglo-Saxon cemeteries suggests that some of their settlements were abandoned and the frontier between the invaders and the native inhabitants pushed back some time around 500.
Anglo-Saxon expansion resumed in the sixth century, although the chronology of its progress is unclear. One of the few individual events which emerges with any clarity before the seventh century is the Battle of Deorham, in 577, a West Saxon victory which led to the capture of Cirencester, Gloucester and Bath, bringing the Anglo-Saxon advance to the Bristol Channel and dividing the Britons in the West Country from those in Wales. The Northumbrian victory at the Battle of Chester around 616 may have had a similar effect in dividing Wales from the Britons of Cumbria.
Gradual Saxon expansion through the West Country continued through the seventh, eighth and ninth centuries. Meanwhile, by the mid-seventh century the Angles had pushed the Britons back to the approximate borders of modern Wales in the west, the Tamar in the South west and expanded northward as far as the River Forth.