1066: England

In January of 1066, Edward the Confessor, King of England died. Since he was childless, their were 4 men immediately began to position themselves to be the next king.

-Harold II, the Earl of Wessex

-William, Duke of Normandy. The year before, Harold II had supposedly promised to support him in his claim to the throne upon Edward's death.

-Harald Hardraada, a Viking from Norway allied with Tostig Godwin, Harold II's brother.

-Edgar the Athleling, a young boy old who was probably the closest related to Edward. Since he was young and wielded no real power, he was ignored by the other parties.

Harold was closest proximity to Edward, and was immediately crowned king. William received the news in Normandy (northern France) and began preparing an invasion force to claim the crown by force from Harold, whom he believed had broken his word.
Harold believed that the oath that he'd sworn to support William as the next king was invalid, since he felt that he'd been coerced and so was not bound to it.
Harald Haardrada the Viking sailed from Norway with a force of over 200 warships, landed in Orkney in the northern part of England to gather more men and supplies, then sailed again to the mouth of the Tyne river to meet up with Tostig, Harold's estranged brother. Together, they marched into Northumbria, burning and pillaging as they went. On September 20 they met and defeated an English force led by two earls (Morcar and Edwin). Then, the invaders withdrew to Stamford Bridge to await surrender conditions for the nearby town of York. On September 25, after a forced march north, Harold II's army met and surprised the forces of Harald Hadraada and Tostig at Stamdford Bridge. Both Harald and Tostig were slain in the battle, and naturally Harald Hadraada's threat to Harold II's reign was extinguished. Harold had no time to celebrate however.
Unbeknowst to Harold II, William had crossed the English Channel and landed with a large Norman force at Pevensy, England on the southern coast. He marched north into Wessex, Harold's private land, and began to terrorize the countryside by burning and pillaging (folks did a lot of burning and pillaging in those days). He probably did this to provoke Harold into rushing down and meeting him on a ground of his own choosing. Whatever the reason, this is exactly what Harold did.

Without waiting to be reinforced by archers or cavalry, he burst onto the scene at Senlac Hill and fought what would become the Battle Hastings.
On October 14, 1066 William, Duke of Normandy defeated the Saxon army under Harold II, and killed him in the process. The Duke of Normandy became known known as William the Conqueror.
Although descended from the Vikings, the Normans had learned much from the French about power, grandeur, and upper class existence, and it influenced England for centuries. William was a harsh yet effective leader. 1066 marks a turning point from Saxon rule in England and much about English culture can be attributed to this year.

Sources:
"A Brief History of: British Kings and Queens" by Mike Ashley
"History of English Speaking Peoples" by Winston Churchill