The term Norwegian Realm (Old Norse: Norégveldi, Bokmål: Norgesveldet, Nynorsk: Noregsveldet) and the Old Kingdom of Norway, refer to the Kingdom of Norway's peak of power at the 13th century after a long period of civil war before 1240. The kingdom was a loosely unified nation including the territory of modern-day Norway, modern-day Swedish territory of Jämtland, Herjedalen, Ranrike and Idre and Särna, as well as Norway's overseas possessions which had been settled by Norwegianseafarers for centuries before being annexed or incorporated into the kingdom as 'tax territories'. To the North, Norway also bordered extensive tax territories on the mainland. Norway, whose expansionalism starts from the very foundation of the Kingdom in 872, reached the peak of its power in the years between 1240 and 1319.
The secular power was at its strongest at the end of King Haakon Haakonsson's reign in 1263. An important element of the period was the ecclesiastical supremacy of the archdiocese of Nidaros from 1152. There are no reliable sources for when Jämtland was placed under the archbishop of Uppsala. Uppsala was established later, and was the third metropolitan diocese in Scandinavia after Lund and Nidaros. The church participated in a political process both before and during the Kalmar Union that aimed at[clarification needed] Swedish side, to establish a position for Sweden in Jämtland. This area had been a borderland in relation to the Swedish kingdom, and probably in some sort of alliance with Trøndelag, just as with Hålogaland.
A unified realm was initiated by King Harald I Fairhair in the 9th century. His efforts in unifying the petty kingdoms of Norway, resulted in the first known Norwegian central government. The country however fragmented soon, and was again collected into one entity in the first half of the 11th century. Norway has been a monarchy since Fairhair, passing through several eras.
Iceland was more reluctant to give up their independent rule, so the Icelandic saga author Snorri Sturluson was given royal invitation to the court of King Haakon Haakonsson and was there convinced that Iceland was by right Norwegian. So began the Age of the Sturlungs, a time of political strife in Iceland, the Sturlungs worked for bringing Iceland to Norwegian rule and spread propaganda through their position at the Althing and even resorted to violence before, in 1262, the Old Covenant was signed, which brought total Norwegian rule over the island.
In Ranríki Konunghella was built as a royal city alongside Túnsberg and Biorgvin. It remained Norwegian until the 1658 Roskilde treaty. Herjárdalr became Norwegian during the 12th century and remained so for five centuries. Jamtaland started paying taxes to Norway during the 13th century and was later absorbed into a part of the mainland territory the same century. It was occupied by the Swedish during the Nordic Seven Years' War, but later returned to Denmark-Norway as a result of the Stettin treaty of 1570. Idre and Særna, Norwegian since the 12th century, were conquered by Sweden during the Hannibal controversy. Ranríki, Herjárdalr, Jamtaland, Idre and Særna were permanently surrendered to Sweden by the Peace of Brömsebro the 13th of August 1645.