In 1066 king Edward the confessor died without any children to inherit the throne of england, this meant that Harold Godwinson was crowned as king despite supposidly promising an oath to william that he would be the next king . However harold faced his position being jeportised because two other determined young men also wanted to be King. These men were Harald Hadrarda and William of Normandy. England was one of the welthiest and most powerfull countrys in the world and all 3 of these men were prepared to do whatever it took to gain the crown.
The only way to decide who was going to be king was to engage in battle .Harold and william both prepared there forces. First Harald hardra from norway invaided england with his viking fleet and fought against harold godwinson at stanford bridge .After the Battle of Stamford Bridge (In which Harald had died,) Harold had news that william had finally invaided and went down to hastings to prepare to fight William, but this was going to be tough, both men were desperate to be next King and there could only be one winner.
In my opinion the main reason to why william won was pinned on luck, Harold eagarly expecting this to happen and he and his army waited on the beach strong and prepared for the norman invaison. William was planning to arrive on the beach and if this had happened Harold would have slaughtered him. Fortunately for William, the sea was too choppy to sail across the channel and so William's army were waiting in Normandy for the weather to improve before crossing. Luckily for william Hadrada invaided up north and therefore Harold went up north. Harold then fought a battle leaving his army in a much weaker position than before.
A major reason to why harold lost was due to his army was exhausted and weakened in numbers. The battle of stanford bridge was a gruesome one with the norsemen refusing to surrender untill the next day were Hardras son Olav agreed to