The brothers Bengt Jönsson Oxenstierna and Nils Jönsson Oxenstierna are selected to serve as co-regents of Sweden at the death, without a direct heir, of Christopher of Bavaria in January 1448.

The Regency period ends with the election of former regent-administrator Karl Knutsson Bonde as King Charles VIII of Sweden, with the intent to reestablish the Kalmar Union under a Swedish crown.

Installed as king of Sweden on June 20, Charles is hailed on June 28 as the new monarch at the Stones of Mora, not far from Uppsala, mostly due to his own military troops being present at the place, against the wishes of the regents.

Count Christian of Oldenbourg was born in February 1426 in Oldenburg to Count Dietrich of Oldenburg, whom he succeeded in 1440 as Count of Oldenburg and Delmenhorst, and his father's second wife, Hedwig of Schleswig and Holstein (Helvig of Schauenburg) , who died in 1436).

Christian has two brothers, Count Moritz V of Delmenhorst (1428–1464) and Count Gerhard VI of Oldenburg and Delmenhorst (1430–1500), and one sister Adelheid.

Christian is a cognatic descendant of King Eric V of Denmark through his second daughter Richeza.

In the power vacuum that arises in the Kalmar Union following the death of its king, Christopher of Bavaria, in January 1448, the throne is first offered by the Statsraad to the most prominent feudal lord of Danish dominions, Duke Adolf VIII of Schleswig-Holstein, but (being relatively old and childless) he had declined and recommended his nephew, Count Christian, who is is elected to the vacant Danish throne as king Christian I on September 1, 1448.

Norway is now faced with the choice between a union with Sweden or Denmark, 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, with both kings gaining support from various factions in the Norwegian Council of the realm.

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

Christian marries Dorothea of Brandenburg, the nineteen-year-old widow of his predecessor King Christopher, and thus dowager queen, on October 28, 1449, in Copenhagen.

Charles is crowned king of Norway in Trondheim’s Nidaros Cathedral on November 20.

However, Christian also continues pursuing his claim to Norway.

The counts of Holstein are more influential than the Swedes and the Norwegians together, and in 1450 make the Danish Privy Council appoint Christian I of Oldenburg as king.

The Swedish nobility now takes 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 has thereby been decided between Denmark and Sweden, and the Norwegian Council is left with only one candidate for the throne.

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

Sweden and Denmark are in state of war against each other from 1451.

Because of devastating warring, a growing opposition against Charles emerges among the nobility in Sweden.

The strongest opponent is the Swedish church, which opposes Charles's efforts to concentrate royal and secular power.

Other opponents are the family group of Oxenstierna and Vasa (House), which had been on the opposing side in the election of the king.

A special treaty of union between Denmark and Norway, drafted in Danish and serving Danish interests but pledging a separate Norse legislature (a promise that will be unkept by Denmark), is signed on August 29 in Bergen.

Norway had of old been a hereditary monarchy, but this had 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 would be elected among the legitimate sons of the previous king, if such existed.

During the next seven decades, struggle for power and the wars between Sweden and Denmark will dominate the union, as Norway slips ever more to the background under the Oldenburg dynasty.