In the power vacuum that arises following the death of the childless King Christopher of Denmark, Sweden and Norway in 1448, Count Christian of Oldenburg, a son of Count Dietrich of Oldenburg and Hedwig of Holstein, a descendant of King Eric V of Denmark had on September 1, 1448, after signing his ascension promissory,been elected to the Danish throne as King Christian I at the assembly in Viborg.

Meanwhile, Sweden had on June 20, 1448 elected Charles Knutsson as kin Charles VIII.

Norway is now faced with the choice between a union with Denmark or Sweden, or electing a separate king.

The latter option is quickly discarded, and a power-struggle ensues between the supporters of Christian of Denmark and Charles of Sweden.

The Norwegian Council of the Realm is divided.

In February 1449, a part of the Council declares in favor of Charles as king, but on June 15 of the same year, a different group of councilors pays homage to Christian.

On November 20, Charles is crowned king of Norway in Trondheim.

However, the Swedish nobility now tes steps to avoid war with Denmark.

In June 1450, the Swedish Council of the Realm forces Charles to renounce his claim on Norway to king Christian.

The question of the Norwegian succession had thereby been decided between Denmark and Sweden, and the Norwegian Council is left with only one candidate for the throne.

In the summer of 1450, Christian sails to Norway with a large fleet, and on August 2 he is crowned king of Norway in Trondheim.

On August 29, a union treaty between Denmark and Norway is signed in Bergen.

Norway had of old been a hereditary monarchy, but this has become less and less a reality, as at the last royal successions, hereditary claims had been bypassed for political reasons.

It is now explicitly stated that Norway, as well as Denmark, is an elective monarchy.

The treaty stipulates that Denmark and Norway should have the same king in perpetuity, and that he will be elected among the legitimate sons of the previous king, if such exist.Charles Knutsson becomes increasingly unpopular as king of Sweden, and is driven into exile in 1457.

Christian achieves his aim of being elected as king of Sweden, thus reestablishing the Kalmar Union.

He receives the power from temporary Swedish regents archbishop Jöns Bengtsson Oxenstierna and lord Erik Axelsson Tott.

However, Sweden being volatile and split by factions (benefits of union being against nationalistic benefits), his reign there ends in 1464 when bishop Kettil Karlsson Vasa is installed as the next regent.

Charles Knutsson is recalled as King of Sweden, although he is later exiled a second time, recalled again and dies during his third term as king.

Christian's final attempt at regaining Sweden ends in in October 1471 in a total military failure at Brunkeberg (outside Stockholm), where he is defeated by the Swedish regent Sten Sture the Elde, who is supported by the Danish-Swedish nobleman's clan the Thott family.