Since 1050, William had been the pretender to the English throne, at the time in the hands of his cousin, Edward the Confessor, who had no descendants. However, he was not the only one to claim the English throne. His most powerful rival was an English count, Harold Godwinson, who was appointed successor by the Edward himself on his deathbed in 1066.
William argued that Edward had promised the throne to him earlier, and that Harold had sworn support. Because of this “betrayal”, the Norman duke activated a military intervention. He prepared a great fleet that set sail from the mouth of the Somme River, and on September 27, 1066, one of the most powerful armies ever seen landed on Pevensey, in the south of England and defeated Harold´s army in the Battle of Hastings on October 14.
Harold had been crowned king of England on January 6, in the new Abbey of Westminster. With the existence of other pretenders, his coronation was not guaranteed. One of these pretenders was his own brother, Tostig. The King of Norway, Harald Hardrada was another claimant, as was his uncle, the Danish king Magnus I.
Tostig launched several attacks along the South Coast of England during May and disembarked in the Isle of Wight, aided by a fleet that his brother-in-law, Baldwin V of Flanders, provided. Tostig wasn´t well received by the locals and after trying his luck in Lincolnshire and near the River Humber, he retired to Scotland.
By this time, William sent an embassy to Harold to remind him of his oath to support his claim for the throne. Harold prepared an army and a fleet to repel William´s attack, and kept boats and troops stationed in the English Channel for most of the summer.
After defeating Tostig and Harald Hardrada, Harold left a great part of his army in the North and marched with the rest of the troops southwards to confront the fearsome Norman army. Upon hearing news of the Norman arrival on the coast, Harold stopped in London and later continued his journey towards Hastings. Although he tried to surprise the Normans, William´s scouts were well aware of his intentions and informed William in time. All sources record that William himself went out leading his troops to confront Harold. Harold had decided to adopt a defensive position in the top of Senlac Hill.
The battle started early on October 14, and lasted all day. English soldiers held up a wall of shields that at first managed to repel the Norman troops to the point that Normans had to back up after heavy losses. Then, the Norman cavalry took the initiative and annihilated the English soldiers. The corpse of Harold was identified after the battle.
William was crowned king of England in London by Christmas. After some necessary arrangements, he returned to Normandy in 1067, although during the following years he had to quash several English military uprisings. These uprisings were not completely over until 1075.