The crisis of 1066 and the subsequent Norman invasion and conquest were the result of the English king, Edward the Confessor, having no children.
The English practice at the time was for the Witan, the council of the chief men of the country both church and lay, to select from the æþelings. The æþelings were the male members of the royal family, and the Witan would chose the one it thought most suitable to be the next King of the English. This was done irrespective of who was the eldest, or who was legitimate, or even if the chosen was a son, nephew, or brother of the previous king.
The problem in 1066 was there was only one æþeling, Edgar. He was King Edward's half brother's grandson and he was about 12 years old at the time. This should, in fact, not have been a problem. Harold Godwinson, the Earl of Wessex, had effectively ruled England on behalf of King Edward for the past 14 years, as had his father, Godwin, for many years before him. Harold had shewn himself to be totally trustworthy on the king's behalf and it had been assumed that he would continue in the role under Edgar until the young man was old enough to rule in his own right. The problem in 1066 lay in the fact that two others had staked a claim to the throne, both of them foreigners.
The first claimant was Harald Hardrada, the King of Norway. His claim was through a promise that his half brother, Magnus, was said to have been given by Harðeknute whilst he was King of the English. Earl Harold's estranged brother, Tosti Godwinson, encouraged Hardrada in his claim.
The other claimant was William the Bastard, Duke of Normandy. He stated that he had a claim through a promise made to him by King Edward the Confessor, who was a cousin on the king's mother's side. William also said that Earl Harold had sworn to promote William's claim on King Edward's death. Unfortunately for William, King Edward had told no-one in England about his desire to have William as his heir. In fact Edward had brought his half brother's son, Edward the Exile to England from Hungary to be his heir. Unfortunately Edward the Exile died soon after his arrival in England, but King Edward had named the Exile's son, Edgar, as Æþeling.
On his deathbed King Edward decided the situation was sufficiently changed to tell the Witan that Harold Godwinson was to be his heir. On Edward's death, the Witan considered the threat from overseas and the grave risk of having a 12-year-old king at such a time, and agreed with the late king's decision and proclaimed Harold King of the English.
In order to counter the double threat of invasion, Harold called out the Wessex Fyrd, the Territorial Army of those days, to watch the Channel coast. Also watching the Channel was the English fleet, led by Edgar the Steersman, one of Bishop Wulfstan of Worcester's men. The northern threat King Harold left to his two brothers-in-law, Earl Edwin of Mercia and Earl Morcar of Northumberland.
Nothing happened until early autumn, by then the Fyrd had been stood down and the fleet called to port to keep it safe from the autumn gales.
The first invasion was that of Harald Hardrada, who had King Harold's brother Tosti with him. Edwin, Morcar and another young earl, Walþeof of Northampton, met up with Hardrada and his Viking army at Fulford in Yorkshire. The young earls and their army fought well, but eventually the experience of Hardrada and his Vikings told and the English army was put to flight. Hardrada and Tosti took the city of York. They demanded that supplies and hostages be brought four days later to a meeting at Stamford Bridge, a few kilometres outside the city.
When they arrived at Stamford Bridge, the hostages were not there. Instead they found King Harold and another English army. Harold and his brother Gryth had gathered their Huscarls, the professional warriors who formed their bodyguard, and ridden north, collecting elements of the Mercian and East Anglian Fyrd as they went. They had covered 320 km in six days. Having caught the Vikings off guard they attacked and thoroughly defeated them, killing Harald Hardrada and Tosti in the process.
Before King Harold and his men could lick their wounds, they received news that William the Bastard had landed and established himself at Hastings in Sussex. Leaving the northern earls to re-form the northern Fyrds, the King and his brother gathered their remaining Huscarls and rode south, sending messages ahead of them to the southern counties to gather their Fyrds. After a short rest in London, King Harold, his brothers Gyrth and Leofwine, together with Huscarls and Fyrdmen, rode south to meet with the men of the Wessex Fyrd at the Hoar Apple Tree on the hills outside Hastings. From there they could guard the roads to London and Winchester, stop the Normans from raiding for supplies and at the same wait for yet more men to join the English army.
William could not wait. He had sailed late in the year, he was living in a hostile land, he had limited supplies and his army was made up of mainly hired troops. At the first opportunity he marched towards the English. King Harold's men had been watching the Normans and the King moved the English army to Senlac Ridge to block the advance. Harold's choice of ground was deliberate as the steepness of the hill prevented the Norman cavalry from charging the English, who always fought on foot. The Battle of Hastings raged all day, with the English holding off all that William could throw at them. Just before dusk William made a final attacked using archers, infantry, and cavalry together. King Harold died, and the English army fell apart. With Harold dead the Huscarls, who would never leave their lord, and all the nobles, fought till they too were killed.
William waited for the English to submit to him and accept him as king. They did not. Instead, the depleted Witan elected Edgar Æþeling King of the English. William burnt a trail of destruction around London until the Witan and Edgar submitted and offered him the crown. William was crowned King of England on Christmas day 1066.
William shortly afterwards returned to Normandy, taking hostages and booty with him. He soon had to go back to England as the English had started to get over the shock of their defeat at the Battle of Hastings and revolts were breaking out. In the year 1067 William had to suppress revolts at Dover, headed by one of his supposed supporters, but backed by the English, the city of Exeter, where the revolt was led by King Harold's family, the Welsh border, where the leader was Edric the Wild, and York. The following year there were uprisings at Durham, and York, with Edric the Wild in league with the Welsh causing havoc in the Marcherlands and King Harold's sons bringing in Norse-Irish pirates to plunder the West Country.
The year 1069 saw Earl Walþeof leading the men of Northumberland in a revolt that later drew in a Danish fleet on behalf of the King of Denmark, Swein Estriðsson, who had a claim to the throne of England. There was also an invasion from Scotland led by Edgar the Æþeling, whose sister was now married to the King of Scots. To make matters worse for William, another resistance leader called, Hereward the Wake, had set himself up on the Isle of Ely and had made the fens around the Wash a 'no go' area for Normans. To try and stop any more revolts in Northumberland whilst he dealt with the other problem areas, William ordered that the land be laid waste and the 'Harrowing of the North' began.
William's treatment of Northumberland drove many to Ely. There they joined Hereward and his Danish allies. Protected by the wetlands of the fens they resisted all William's efforts to beat them. The fall of the Isle of Ely did not come until 1071 and followed William's crushing of a revolt by Edwin and Morcar, who had had their earldoms taken from them. Morcar was at Ely when it surrendered and was taken prisoner. Edwin fled Ely, only to be betrayed and murdered. Hereward and his men escaped and continued to fight on.
By 1072 things had settled down sufficiently in England for William to invade Scotland and gain the submission of Malcolm, King of Scots. Part of the deal was that Malcolm would expel Edgar Æþeling and stop supporting cross border raids by English exiles now living in Scotland. Things continued quiet in 1073 and William took an Anglo-Norman army to France to quell a revolt in one of William's continental fiefdoms. In fact, there were no major problems in England until 1075. In that year two Earls, who both had English blood but had fought for William at the Battle of Hastings, revolted. However, instead of rising together, Roger of Hereford revolted first and was crushed before his brother-in-law, Ralf of East Anglia, got going. The Revolt of the Earls was easily taken care of, but a final blow for the English was the execution for treason of Earl Walþeof, who had been implicated in the revolt. Walþeof was the last of the true English Earls.
In 1077 Malcolm, King of Scots, together with an army of English exiles crossed the border and created havoc in the north of England before being pushed back by King William's son, Robert Curthose.
The last major uprising by the English against William and his Normans was in 1080, when the men of Gateshead in County Durham, slew the Bishop and his Norman troops. William was in Normandy at the time and the revolt was put down by his half brother, Bishop Odo, Earl of Kent. Odo harrowed the north yet again.
It could be said that, with that final act of devastation, the Norman Conquest was complete. When the Domesday Survey was undertaken in 1085 it shewed the massive amount of the country that had been either laid waste or heavily damaged by the Conquest. It also shewed the almost complete transfer of land from English hands to those of the Normans and their Breton, French and Flemish mercenaries.
As a result of the Norman Conquest, the English monarchy, English government, church, society, language and outlook changed forever.