Before the Normans England was reached by another population, the Vikings, who in the 8th century settled/raided/invaded the large areas in the north and in the east of England, as well as the islands. This new wave of invaders came from Scandinavian countries (Norway, Denmark). When they settled in Britain there were some conflicts between Anglo Saxons and Vikings. In the 9th century peace was reached with the intervention of King Alfred the Great, king of Wessex, an Anglo Saxon king.
The agreement/deal between the two populations was achieved at the cost of leaving a large part of the country under the control of the Vikings (north and east). In this period there were also Viking kings such as King Canute, who was one of the few Viking kings that ruled Britain in this period. This situation shows that the Vikings weren't only invaders but they also integrated with Anglo Saxons.
In 1040 immediately before the arrival of William, the throne was given back to the Anglo Saxons when a Saxon king Edward, known as/named as The Confessor succeeded to the throne of Britain. He was named Confessor because his main interest was religion and not so much politics. In spite of the fact that he wasn't interested in ruling/governing the country, he had strong familiar links with Normandy and for this reason, he had spent most of his life there where he also moved.
In 1066 William died and the Royal Council (a new institution introduced by Anglo Saxons, it’s the ancestor of the present democratic parliament, the representatives were warriors and religious figures and they had the task to advice the king and elect him) chose King Harold, who came from a Wessex family (the most important reign in Britain) but at the same time as Harold was in the northern border to defend his lands from the attacks/raids of the Vikings, William landed on the south coast of England with an army and defeated the Anglo Saxons in an important battle which was concluded on 14th of October of 1066 at Hastings. He could claim the throne because he was a relative of Edward The Confessor’s. He was ambitious, he wasn't satisfied with his position as Duke of Normandy, he wanted to be king. In 1066 the Norman age started and the country passed to the Normans, William and his court/Norman followers took possession of the country. He was coronated /crowned king on Christmas’ day of 1066.