The Angles and Saxons came to Britain first (from what is now Denmark and Saxony) as mercenaries under the British High King Vortigern, helping him defend the Roman province of Britannia against Pictish and Irish raiders when it had been left defenceless by the withdrawal of Roman troops following the collapse of the Western Empire.
However, seeing that Britain could not defend itself against them, they brought their families and tribes and clans with them and they settled. Over the course of the 5th-7th centuries, they ousted the native population from vast swathes of land that now became English and Saxon kingdoms, the English or Angles in East Anglia, the Midlands and Northumbria, the Saxons in Essex and right across the south.
The native Britons either fled to Wales (Wales, from the Saxon word for foreigners, which then stretched all the way up the west coast as far as Strathclyde) or south across the sea to the part of modern France ever since known as Britanny; or they remained among the Saxons as slaves, landless in what was once their own land.
The incomers only setback was when a British leader (presumably Arthur) defeated them so thoroughly at Mons Badonicus (c.AD496) that for fifty to a hundred years certain parts, notably what are now Wessex and Essex (including London and Colchester) became British again.
Despite that, colonisation and settlement was inexorable. During the five hundred years that led up to the Norman Conquest and the imposition of a Norman-French culture which was, at first at least, no more than a veneer, England became England. The little kingdoms like Kent and Sussex and Essex became united with their more powerful neighbours, and even those powerful neighbours had to unite finally in the face of a new common enemy. Wessex turned out to be the winner, mainly because Danes were invading the country in the north and Wessex was left as what Bernard Cornwell calls The Last Kingdom in his new trilogy set among Saxons in the 9th century, and when Alfred defeated the Danes he and his successors became kings of the whole country.
Speaking of Cornwell, at one point in The Last Kingdom he sums up Anglo-Saxon society in such a brief, clear and masterly way that I am going to quote it here.
There is a hierarchy among men [...] At the top is the king, and beneath him are his sons, and then come the Ealdormen who are the chief nobles of the land and without land a man cannot be noble, though I was, because I have never abandoned my claim to Bebbanburg. The king and his Ealdormen are the power of a kingdom, the men who hold great lands and raise the armies, and beneath them are the lesser nobles, usually called reeves, and they are responsible for law in a lord's land, though a man can cease to be a reeve if he displeases his lord. The reeves are drawn from the ranks of thegns, who are wealthy men who can lead followers to war, but who lack the wide holdings of noblemen like Odda or my father. Beneath the thegns are the ceorls, who are all free men, but if a ceorl loses his livelihood then he could well become a slave, which is the bottom of the dungheap. Slaves can be, and often are, freed, though unless a slave's lord gives him land or money he will soon be a slave again.
One of Alfred's "achievements" was to impose the Roman Christian religion on a still largely non-Christian population. The Angles and Saxons arrived in Britain as worshippers of the Earth Mother, Nerthus, and of Woden, Thunor and Tiw, and the goddess Frig, after whom four of our days of the week and many places are named. (See Kathleen Herbert's wonderful little book on the Lost Gods of England.)
They also believed in Fate, in the Three Weird Sisters, and a whole world of magic and shamanism - the world which in many ways underlies the world of Tolkein's books, and is excellently described and explained in Brian Bates' The Way of Wyrd and The Real Middle Earth, both reviewed on this site.
The best general history is in my view still Penguin's The Anglo-Saxons, but I also recommend (especially for writers!) The Year 1000, in which the authors take us through the year, showing us how life was lived, month by month, before the Norman invasion.
Finally, of course, there is the Venerable Bede himself, the "Father of English History", an English monk born in Northumbria in 673 whose Ecclesiastical History of the English People gives us a truly authentic picture of the birth of a nation. Read it: it is slow, yes, but it is quite unforgettable.
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READ THE SHORT STORY "WIHTRED THE UNLUCKY" by JAY WICKMAN
(murder among the East Saxons in the 7th century)