This is how I formulated it: 'Effectively' is the key word here. You've got to remember that Magnus was chosen as king by Danish and Norwegian lords. Harald rose in power in Norway quickly after returning from his travels, but never had any power over Denmark. The Danish lords did not choose Harald. Magnus was pressured into accepting joint rule with Harald very shortly before Magnus' own rule ended. Another important thing that has not been mentioned, is that Harald actually allied himself with Svend during the initial Magnus-Svend conflict. Magnus, pressured by his own people, offered Harald the position of fellow king and Harald accepted. This only added to Danish resentment towards Harald after the death of Magnus. If Harald had any power over Denmark he would have been king of Denmark after the death of Magnus, which he wasn't. There is no doubt that Harald wanted to be king of Denmark too and he did invade Denmark after the death of Magnus - resulting in a terribly bloody war. One of Harald's reasons for laying waste to Denmark was to display Svend's inability to protect his own lands. As you correcly pointed out, Harald wreaked havoc in Denmark the following years. Denmark was still recovering from the void and political strife that arose after the death of Canute. There is no doubt that Harald Hårderåde was a badass and a powerful king, but he never was king of Denmark. He simply wasn't! Saying that he was is a simplification that is far worse than those I have made and apologised for earlier in this thread. He was definitely a great personality, and has rightly been called 'the last Viking'.