The Dark Ages
Invaders like the Romans in the 1st Century and the Normans in the 11th Century made their entrance into British history at the south coast. The Romans are usually thought to have made landfall near Sandwich (but it might possibly have been as far west as Chichester or even Southampton) while the Normans put in at Pevensey. The decisive Battle of Hastings occurred outside of Hastings by about five miles, on the site of the current village of Battle, where William then had a monastery built as penance (imposed by the Pope for the killing of so many of the English). Allegedly, the high altar was located over the spot where King Harold died.
The Romans departed early in the 5th Century and Britain was left to its own devices as the empire withdrew to gird its loins against invasive pressure from elsewhere. Britain was a far outpost that was too much trouble, anyway, with local agita ever a possibility (particularly in the north).
Until fairly recently, common belief was that the abandoned Britons forsook remaining Roman culture, returned to something like a fully agrarian existence and were beset by the invasion of Angles, Saxons and Jutes, whereupon they retreated to the extreme west of the land or, indeed, even to Brittany across the Channel.
Contemporary written English history of these "Dark Ages" is in short supply, with some gaps not filled until up to half-a-century later (or more) by the likes of Geoffrey of Monmouth (and then rather fancifully with the growth of Arthurian legend).
According to a monk, Gildas, writing in the 6th Century, the Anglo-Saxons may have first arrived in Britain making a treaty, exchanging supplies and toleration of their presence for military protection from Pictish attack from the north, with subsequent bad faith in dealings resulting in settlement with violence.
Broadly speaking, it's the narrative of resisted invasion that was taught at school when I was young and, until even very recently, the one I had accepted without much thought to challenge.
At odds with that, modern archaeology, DNA examination and other techniques suggest that such reported conflict may have been exaggerated, with apparently little evidence for major battles and rather more suggestion of integrated settlement. That western areas in the north and south were more evidently not Saxon may simply be indicative of the Saxons settling quickly in the east, rather than suggesting ethnic cleansing. Where that leaves Hengist and Horsa, legendary Saxon warlords, or Britonnic King Vortigern who is said to have invited them to Britain, is anybody's guess, though the Battle of Badon appears to be accepted by scholarship (but without King Arthur's participation).
Danes (or Norsemen/Vikings) arrived from the late 8th Century, striking the length of the east coast. Beginning notably with an attack on Lindisfarne/Holy Island off Northumberland in 793, assaults continued, but the attackers didn't pitch up for any length of time until the winter of 854, when they made camp in the Isle of Thanet in Kent, followed shortly after by later encampment on the Kentish Isle of Sheppey, both on the southern side of the Thames estuary.
Building mainly in wood or other perishable materials, post-Roman but pre-Norman cultures left relatively few architectural remains except—in their post-pagan phase—some Saxon churches built of stone. The Romans (arriving before the Anglo-Saxons and Danes) and the Normans (arriving afterwards) more regularly used permanent materials in addition to wood: stone, brick and concrete in the case of the former and stone in the latter, when their invasions were secured. There is a wooden Saxon church surviving at Greensted in Essex, with timbers dating to just before the Norman Conquest, alleged to be the oldest wooden church in the world. It's interesting that the Saxons—used to building in timber—apparently carried those techniques into their later crafting of stone.
As mentioned, Norse incursions initially consisted of piratical raids but, eventually, they settled in numbers. There followed some push-me-pull-you for quite some time between the Saxons and Danes in the possession and rule of England, with the Saxon House of Wessex and the House of Denmark each gaining ascendency a couple of times between the reigns of Saxon King Alfred ("The Great", founder of the first dynasty to rule the whole of Saxon England) and the later Saxon king, Edward the Confessor's 1042 re-establishment of the House of Wessex. There are some colourful and resonant names from both sides in between, in addition to the aforementioned Alfred (founder of the English navy and alleged cake burner): Æthelred the Unready, the Dane Canute/Cnut (also known as "The Great", he was not only king of Saxon- and Danish-held England, but also both Denmark and Norway. He's the geezer alleged to have ordered the waves of the sea to retreat) and his son Harthacnut (is better than none).
Edward the Confessor, founder of Westminster Abbey, having taken an oath of chastity, died without issue and so created the problem resulting in the Norman invasion of England in 1066, under William the Bastard, Duke of Normandy. Edward was succeeded immediately on his earthly departure by Harold Godwinson, whose claim to the English crown was that, in extremis, Edward nominated him as his successor, an appointment agreed by the Witan, the Anglo-Saxon ruling assembly. William's counterclaim was that the dead king had earlier promised him the crown (in 1064), and that Harold had already sworn to support William's claim. Just to stir the pot further, Harald Hardrada, then King of Norway, also laid claim to England (spuriously based on somebody else's pact with Harthacnut) so, in 1066, Harold had his hands full with both Harald (supported by Harold's own disaffected brother Tostig) and William, each planning separate invasions of conquest in support of their kingly claims. Harold marched an army up to Yorkshire and met Harald in battle (at Stamford Bridge), ending not only the Norwegian's claim to the throne but also Harald's and Tostig's mortal existence. Harold then had to march his army southward again to meet the threat from William (about 400 miles round trip with a big punch-up at one end and only a second to look forward to at the other). The rest is history, and William the Bastard became William the Conqueror. The 1066 invasion was, in fact, the last successful hurrah for Norsemen striving for dominance in England: William's Normans were—at least in part— descendants of Danish invaders of northern France.
History's not about conquest and battles in contemporary education, it's about ordinary people's lives. And of course, there's truth in that. All the same I remember learning about this, and drawing maps, at about ten-years-old. I found it thrilling. History now may not be felt to be about battles and their victors (who were mainly ambitious thugs, no doubt), but, in those violent faraway days, the important social and political changes often came as a result of conflict, so it does actually remain significant. I can't help thinking that education, on the whole, was better in my youth but I appreciate that I'm likely to be biased. I might just be too affected by nostalgia for BBC Radio for Schools, that also gave us serialisations of Beowulf, The Odyssey and the legends of Robin Hood and King Arthur, as well as exposure to the canon of English folk music. It's good that other things are taught, but a pity that those once-traditional things are not.