After ascending the throne, Alfred spent several years fighting Viking invasions. He won a decisive victory in the Battle of Edington in 878 and made an agreement with the Vikings, creating what was known as the Danelaw in the North of England. Alfred also oversaw the conversion of Viking leader Guthrum to Christianity. He defended his kingdom against the Viking attempt at conquest, becoming the dominant ruler in England. Details of his life are described in a work by 9th-century Welsh scholar and bishop Asser.