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Conquest of England

Among the allies of Denmark was Bolesław I the Brave, the duke of Poland (later crowned king) and a relative to the Danish royal house. He lent some Polish troops, likely to have been a pledge made to Cnut and his brother Harald when, in the winter, they "went amongst the Wends " to fetch their mother back to the Danish court. She had been sent away by their father after the death of the Swedish king Eric the Victorious in 995, and his marriage to Sigrid the Haughty, the Swedish queen mother. This wedlock formed a strong alliance between the successor to the throne of Sweden, Olof Skötkonung, and the rulers of Denmark, his in-laws. Swedes were certainly among the allies in the English conquest. Another in-law to the Danish royal house, Eiríkr Hákonarson, was the earl of Lade and the co-ruler of Norway with his brother Sweyn Haakonsson – Norway having been under Danish sovereignty since the Battle of Svolder, in 999. Eiríkr's participation in the invasion left his son Hakon to rule Norway, with Sweyn.

In the summer of 1015, Cnut's fleet set sail for England with a Danish army of perhaps 10,000 in 200 longships. Cnut was at the head of an array of Vikings from all over Scandinavia. The invading army was composed primarily of mercenaries. The invasion force was to engage in often close and grisly warfare with the English for the next fourteen months. Practically all of the battles were fought against the eldest son of Æthelred, Edmund Ironside.