House of Knýtlinga in the context of "State formation"

Harthacnut (c. 1018 – 8 June 1042) was King of Denmark from 1035, and King of England from 1040 until his death in 1042. He was the last monarch of the North Sea Empire, an empire consisting of England and Denmark, and was also the last monarch of the House of Knýtlinga.

Harthacnut was the son of King Cnut the Great, who ruled Denmark, Norway, and England, and Emma of Normandy. After Cnut's death in 1035, Harthacnut faced challenges in retaining his father's territories. Magnus I seized control of Norway, while Harthacnut succeeded as King of Denmark. In 1040, following the death of his half-brother Harold Harefoot, he became King of England. Harthacnut died suddenly in 1042 and was succeeded by Magnus in Denmark and Edward the Confessor in England. He was the last Dane to rule England.

Estrid Svendsdatter of Denmark (also known as Estrith or Astrith; sometimes called Margaret; fl. 1017–1032; c. 990s – after 1057 and before 1073) was a prominent Danish princess and titular queen of the Jelling dynasty, half-sister of Cnut the Great and wife of the magnate Ulf Jarl. She was the mother of Sweyn II Estridsen, during whose reign she was commonly styled dronning (“queen”) in Denmark, though she was never queen regnant nor a king's consort. Through Estrid, Sweyn traced his claim to the Danish throne and founded the matronymic House of Estridsen, which ruled from 1047 to 1412.

Medieval sources diverge on several points of her life. She was a daughter of Sweyn Forkbeard, but her mother is variously identified in sources as Sigrid the Haughty or, in earlier scholarship, as the Slavic princess sometimes called Gunhild of Wenden, a view now generally rejected. After Sweyn's death in 1014, Estrid came under Cnut's guardianship. He married her to a son of Grand Prince Vladimir the Great or Yaroslav the Wise, but the prince died shortly afterwards. Several western chroniclers, including Rodulfus Glaber and Adam of Bremen, record a proposed or short-lived marriage with the duke of Normandy (probably Robert I, Duke of Normandy), though the precise details remain uncertain. By the early 1020s, she was married to the English magnate Ulf Thorgilsson, who later served as regent in Denmark. By marriage she was thus, successively, a Russian princess, duchess of Normandy and a Danish noblewoman.