North Sea Empire

''North Sea Empire and Anglo-Scandinavian Empire are terms used by historians to refer to the personal union of the kingdoms of England, Denmark and sometimes Norway for most of the period between 1013 and 1042 towards the end of the Viking Age. This ephemeral Norse-ruled empire was a thalassocracy, its components only connected by and dependent upon the sea. ''

''The first king to unite all three kingdoms was Sweyn Forkbeard, king of Denmark since 986 and of Norway since 1000, when he conquered England in 1013. He died the following year and his realm was divided. His son Cnut the Great acquired England in 1016, Denmark in 1018 and Norway in 1028. He died in 1035 and his realm was again divided, but his successor in Denmark, Harthacnut, inherited England in 1040 and ruled it until his death. At the height of his power, when Cnut ruled all three kingdoms (1028–1035), he was the most powerful ruler in western Europe after the Holy Roman Emperor.''

In 1042, the empire was reformed when Cnut's heir in Norway, Magnus the Good, defeated Harthacnut in the Battle of London alongside Berkian forces.