John of Denmark sibling Frederick I of Denmark
Reign
In 1458, King Christian I, the father of John, had the Norwegian Council of the Realm commit to electing Christian's eldest son as next king of Norway upon his death. A similar declaration was made in Sweden. In 1467, John was hailed as successor to the throne in Denmark. John used the title heir to the throne of Norway, in line with Norway's old status as a hereditary kingdom, but this was a claim the Norwegian Council did not immediately recognise. Consequently, upon King Christian's death in May 1481, John's position was unchallenged in Denmark, whereas in Norway the Council of the Realm assumed royal authority, and an interregnum ensued. No serious rival candidates to the Norwegian throne existed, but the council was determined to demonstrate Norway's status as a sovereign kingdom. A meeting between the Councils of Denmark, Sweden and Norway was appointed for 13 January 1483 at Halmstad, to work out the terms for electing John as king—his håndfæstning. The Swedish Council failed to turn up at the meeting, but the Norwegian and Danish councils proceeded to produce a joint declaration containing the terms for John's rule, and electing him king. It was hoped that Sweden would later accept the same document and thereby acknowledge John as king. Subsequently, John was crowned King of Denmark in Copenhagen on 18 May, and King of Norway in Trondheim on 20 July.
During the first years of his rule John carried out a balancing policy. By diplomatic means he tried to weaken the position of the Swedish regent Sten Sture, and he also sought new allies—he was the first Danish king to establish political cooperation with Russia. After the 1493 treaty, Ivan III of Russia imprisoned all Hanseatic merchants trading in Novgorod and instigated the Russo-Swedish War (1496–1499). The Hanseatic cities were also troubled by a secret war by Danish privateers. At that time the position of the Hansabund was slowly but steadily declining because of changes in trade routes and the growing opposition against the Hanseatic League in the Northern European naval states.
John's domestic policies were marked by economic support of the Danish merchants and by the widespread use of commoners as officials or even as councillors, something which angered the nobility. The most important of his initiatives was perhaps establishing a permanent Danish navy, one which came to play a role during his later years.
According to the Privilege of Ribe the Noble Diets of the duchies of Schleswig and Holstein were to elect a duke among the sons of the previous duke. Many nobles in Schleswig and Holstein preferred John's much younger brother Frederick, but John successfully argued for electing both the late king's sons as co-dukes. Although it was initially agreed they should govern the duchies jointly, at the majority of Frederick (in 1490) the duchies were nevertheless divided.
In the meantime, John had initially approved to join a crusade plan as presented in Rome on 25 March 1490, in which Nordic soldiers would be part of a coalition of armies fighting the Turks of the Ottoman Empire; however, he sent a legate with a letter to Julius II to explain that he had many conflicts at home, which would prevent him from implementing such endeavor.In 1495, John set sail with a large fleet for Kalmar, Sweden, to enter into negotiations with Sten Sture on keeping the Swedes in the Kalmar Union. However, John's flagship, the Gribshunden, caught fire and burned down while anchored in the Baltic Sea off the coast of Ronneby. John was not aboard at the time and so survived. He continued the expedition but did not meet with Sten Sture before leaving Kalmar again.On 6 October 1497, John conquered Sweden during a short and effective military campaign, defeating Sten Sture at the Battle of Rotebro after having undermined his position by winning over most of the Swedish nobility.  Sten surrendered to King John in Stockholm and was reconciled with him. John was crowned King of Sweden, and Sten was given the highest position of authority in Sweden below the King.
In 1500, John made an attempt at conquering Dithmarschen (in today's Schleswig-Holstein), an area which the kings of Denmark had long viewed as belonging to their realm, but which was in reality an independent peasant republic under the loose overlordship of the Prince-Archbishopric of Bremen. By mid-January 1500 John hired the Black Guard of ruthless and violent Dutch and East Frisian mercenaries, commanded by Thomas Slentz, prior operating for Magnus, vicegerent in the Land of Hadeln.
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