Canute proceeded to England in the summer of 1015 with a Danish force of approximately 10,000 men. This time, he was joined by his Norwegian brother-in-law Eiríkr Hákonarson, who was an experienced soldier and statesman. Fortunately for Canute, a strong mercenary chief, Thorkell the High, pledged alliegance to him. The Earl Eadric also joined the Danes with forty ships.
The invasion force landed in Essex, which was occupied quickly. Northumbria fell next, and Canute executed its Earl Uhtred for breaking an oath pledged to Sweyn Forkbeard two years earlier. In April 1016, Canute entered the Thames with his fleet and besieged London. King Ethelred died suddenly during the siege, and his son Edmund Ironside was proclaimed king. When Edmund left London to raise an army in the countryside, he was intercepted by Canute at Ashingdon, Essex. After a decisive victory for Canute in the Battle of Ashingdon, Edmund was forced to negotiate under unfavourable circumstances.
Meeting on an island in the Severn River, King Edmund II was forced to accept defeat and sign a treaty with Canute in which all of England except for Wessex would be controlled by Canute, and when one of the kings should die, the other king would take all of England; his sons being the heir to the throne. After Edmund's death (possibly murder) on 30 November, Canute ruled the whole kingdom. Canute was recognised by the nobility as the sole king in January 1017.