For a few Viking years, England, Denmark and Norway shared one king
Between 1013 and 1042, England, Denmark and Norway were mostly ruled as one realm held together only by the sea. At its peak under Cnut the Great, from 1028 to 1035, only the Holy Roman Emperor outranked its king among western European rulers.
Cnut's father, Sweyn Forkbeard, already king of Denmark and Norway, conquered England in 1013 but died early the next year. English nobles recalled the exiled Æthelred, and Cnut sailed home. His brother Harald now held Denmark, so Cnut raised his own fleet with promises of plunder and returned in 1015. After Æthelred died in April 1016, Londoners backed his son Edmund while nobles swore loyalty to Cnut. Following a Danish victory at Assandun, the rivals split the kingdom along the Thames, until Edmund's death that November left Cnut sole king.
He married Æthelred's widow Emma in 1017, though he already had an English wife, divided England into four earldoms on the Scandinavian pattern, and agreed at Oxford to rule under the laws of King Edgar. When Harald died childless he claimed Denmark in 1019. Rivals in Norway and Sweden attacked Denmark, but after the Battle of the Helgeå, whose winner the sources dispute, Cnut sailed with 50 ships in 1028, collected oaths from Norwegian chieftains and was acclaimed king at Nidaros, today's Trondheim. Coins even styled him king of the Swedes, possibly boasting more than fact.
In 1027 he travelled to Rome for Conrad II's imperial coronation, part penance and part diplomacy. He won lower tolls for northern pilgrims, persuaded the emperor to return Schleswig to Denmark, and arranged for his daughter Gunnhild to marry the emperor's son. He also forced three Scottish kings, including Malcolm, into vassalage. As a zealous patron of the Church in England, he gained a standing among Christian rulers that no earlier Scandinavian king had enjoyed.
The union was fragile. Cnut ruled from England, leaving regents in Denmark whose loyalty he doubted, and by his death his inner circle was English, led by Godwin, Earl of Wessex. Historians coined the name North Sea Empire only in the early 20th century, though John Speed treated Cnut's lands as an empire in 1623. After Cnut died in 1035 the realm split; his son Harthacnut briefly reunited England and Denmark from 1040 until 1042.
Source: North Sea Empire
