Already king of Denmark and Norway, in 1013 Sweyn I overthrew King Aethelred 'The Unready' of Wessex, and took control of England as well. This brief Danish rule over the entirety of the land was to last only a few months, as Sweyn died on 3rd February 1014. His son Cnut was unable to hold on to power, and Aetheldred reclaimed his kingdom. However, Cnut returned in 1016, and inaugurated the most prolonged period of Danish rule of England, lasting for the next 26 years.
Editors. "King Sweyn returns; accepted as King by the Danelaw". The Literary Encyclopedia. First published 31 July 2012
[http://www.litencyc.com/php/stopics.php?rec=true&UID=1946, accessed 26 November 2015.]