Cnut III of Denmark (The Kalmar Union)

Harthacnut, Cnut III, was the first child of Cnut I (II) and his second wife, Emma of Normandy, and would succeed his father as King of Denmark.

With constant threats to Denmark from Hordaland and Gothenland Cnut decided to strengthen his rule in Denmark and in 1026 installed Harthacnut as his regent there, backed by his brother-in-law Earl Ulf. However it soon appeared that Ulf was issuing laws without reference to Cnut's kingship and this forced Cnut to re-invade and remove Ulf from power. Whatever Harthacnut's part in this scheme was it was forgiven.

Unlike his half-brother Sveinn in Viken, Harthacnut's reign did not come under severe opposition until its later years and he succeeded to full-rule upon his father's death in 1032 with little trouble.

He was immediately actively planning to remove his half-brother Harald I and claim Anglia for himself and frequently threatened invasion. However the only concrete attempt ended in failure as Edward III of Wessex rallied to Harald I's side and defeated the Danish army in 1036. Other attempts were frustrated by issues closer to home he would never face his half-brother on the battlefield.

He did however have to face Magnus I of Hordaland, who had already evicted Sveinn from Viken and expelled all the Danes from Norway. Once Sveinn died, Viken passed to Harthacnut by de facto birthright - Harald I was in no position to oppose - and he immediately began campaigns against Magnus. These did not go entirely to plan and by 1039 defeat had forced Harthacnut into making Magnus his heir. Repeated taxations to pay for the unsuccessful schemes made him unpopular and he was lucky to be untroubled by a major revolt.

That Harthacnut seemed to be plagued by ill-health was probably well-known by his contemporaries. His mother Emma was quick to switch her efforts to regain the Anglian throne to her older sons Edward and Alfred. And his nobles willingness to accept Magnus I as king may have been in part because they did not expect Harthacnut to live long enough to sire an heir.

In 1042 Harthacnut died, suddenly, and as had been agreed, Magnus I succeeded, uniting Hordaland, Viken and Denmark for a brief few years. It would be Harthacnut's cousin Sweyn II who would restore Danish rule to Denmark and usher in a new and lasting dynasty.