Sweyn Forkbeard, son of Harald Bluetooth and King of Denmark and part of Norway, invaded England in 1013 driving out the English King Ethelred II (“The Unready”) and his family who fled to Normandy.

Sweyn was proclaimed King, but died on the 3rd February 1014. Though the Danes wanted Sweyn’s son, Cnut, to take over, the English council invited Ethelred to return to his kingdom under new terms. On his homecoming, Ethelred took a large army to challenge Cnut, who was in Gainsborough, but Cnut withdrew and returned to Denmark, abandoning his English supporters.

In September 1015, Cnut invaded England with a substantial fleet, initially landing in Sandwich, Kent. He then sailed around to the river Frome, and ravaged the land through Dorset, Wiltshire and Somerset, staying in Wessex for the winter, enticing some Englishmen to defect to him, most significantly Eadric Streona, the ealdorman of Mercia. This was not a straightforward invasion – it involved a considerable amount of English support for Cnut's candidacy.

In the new year 1016, with Eadric Streona's forces, Cnut led his army over the Thames at Cricklade and went into Mercia, passing into Warwickshire and massacring everyone they met. One of King Ethelred's sons, Edmund Ironside, having married the widow of Earl Sigeferth of the Five Boroughs (Derby, Leicester, Lincoln, Nottingham and Stamford), was in the territory receiving its submission and raising an army to confront Cnut. Edmund had become the leader of English resistance to the Danes as his father, Ethelred, was in ailing health.

In Northumbria, Edmund enlisted the support of its ealdorman, Uhtred, who gathered an army there and then the two leaders advanced south. Meanwhile, Cnut continued to pillage in southern England and the East Midlands. Edmund and Uhtred failed to bring Cnut to battle, and when the West Saxons along with the Mercians submitted to Cnut, and Cnut had gone northwards to subdue Yorkshire, Uhtred and Edmund split their forces. Uhtred returned to Northumbria and submitted to Cnut, who had him executed; Edmund returned to the stronghold of London to be with his father.

Ethelred died on the 23^rd April 1016. The councillors who were in London chose Edmund to be king, and he went to Wessex to force the submission of the West Saxons. Meanwhile, at Southampton, an important group of English nobles, including Eadric Streona, declared for Cnut.

In May, Cnut brought his fleet into the Thames and besieged London. After several failed attacks, Cnut raised the siege and marched into Wessex to find Edmund. They met at Penselwood on the Wiltshire-Dorset-Somerset borders (near Gillingham) where an inconclusive battle took place.

Late in June, the two armies met again at Sherston, near Malmsbury in Wiltshire, with much slaughter on both sides. Cnut slipped away and returned to London, which he once again put under siege. Edmund gathered another army in Wessex, and marched to London driving the Danes back to their ships. Two days later, Edmund led his army across the Thames at Brentford, and defeated Cnut’s forces albeit suffering heavy losses of his own. He returned to Wessex to raise another army. In the meantime, Cnut besieged London once more, but was still unable to take the city.

Cnut then sailed with his army up the Essex coast and into the River Orwell from where he proceeded across country to Mercia, pillaging and gathering supplies before returning to his ships and crossing the Medway. Edmund once more led an army against them and fought a battle at Otford in Kent, defeating the Danes and driving them back to their base on the Isle of Sheppey. At this point, Eadric Streona of Mercia swapped sides and Edmund unwisely received him back, for it was Eadric's treachery which led to Edmund's final defeat in battle on a hill called Assandun in Essex on 18 October 1016.