King Magnus VII rules Norway until 1350, when his son, Haakon, is placed on the throne as Haakon VI.

In 1363, Haakon VI marries Margaret, the daughter of King Valdemar IV of Denmark.

Upon the death of Haakon VI, in 1379, his son, Olaf IV, is only ten years old.

Olaf had already been elected to the throne of Denmark, as Olaf II, on May 3, 1376.

Thus, upon Olaf's accession to the throne of Norway, Denmark and Norway enter personal union.

Olaf's mother and Haakon's widow, Queen Margaret, manages the foreign affairs of Denmark and Norway during the minority of Olaf.

King Magnus VII leaves Norway to his son and successor, Haakon VI, in 1355; he lives hereafter in Sweden, where he will fight constantly with the powerful aristocracy.

Haakon, born in 1340 (possibly in mid-August), most likely in Sweden, though the exact date and location of his birth remain unknown, is the younger son of Magnus Eriksson, king of Sweden and Norway, and Blanche of Namur.

His older brother Eric is a rival king of Sweden in opposition to his father between 1356 and 1359.

Haakon and his paternal family belong to the Swedish House of Bjelbo, which had succeeded the House of Eric in Sweden and the House of Sverre in Norway.

Haakon is a great-grandson of Haakon V of Norway through his only legitimate daughter, Ingeborg, and is considered an acceptable heir to the throne by the Norwegian nobility.

Another noteworthy ancestor of Haakon, through his paternal grandfather Eric Magnusson, Duke of Södermanland, is Magnus III of Sweden.

Haakon had been raised in Norway to prepare the young prince to later rule the kingdom in his own right.

During the early autumn of 1343, the most prominent members of the Norwegian Council of the Realm attended a meeting with Magnus at Varberg Castle.

Letters were issued throughout Norway and Sweden on August 15, 1343, stating that the King and the Council had decided to place Haakon on the throne of Norway.

Representatives of the cities and the general public had assembled barely a year later at Båhus Castle, where they hailed Haakon as their king and took the oath of perpetual fealty and servitude to him.

Though the meeting at Båhus Castle forged historic ties to the old elective monarchy in Norway, the acclamation documents created by the Council of the Realm stipulated that Haakon was to rule over only parts of Norway, and it was also carefully documented that the Norwegian Law of Succession would apply if he were to die leaving no legitimate son, thereby ensuring that the hereditary monarchy would be upheld.

The next in line to the Norwegian throne would then be his older brother Eric and his descendants, but the provision becomes moot when Eric dies in 1359.

The meetings at Varberg Castle in 1343 and at Båhus Castle in 1344 were later properly ratified in another meeting in the port city of Bergen as late as 1350.

Magnus had abdicated his Norwegian throne sometime between August 8 and 18 in 1355.

Haakon then ruled as the sole king in the kingdom, though his father continued to exercise control over Norway in the following years, albeit no longer in name.

The first documented event in which Haakon acted as sole king and ruler over his kingdom was on January 22, 1358, when he sent a letter of approval for the privileges in the capital city of Oslo.Norway in 1355 had actually been partitioned between Haakon and Magnus: Magnus had specifically requested the territories of Hålogaland and the Norwegian islands in the North Sea at the ratification meeting in Bergen in 1350.

Magnus additionally holds the territories of Tønsberg and Skien, and he is also the real ruler over the territories of Borgar and most of Bohuslän, which are held as personal fiefs by Queen Blanche.

Because of this, the realm of Magnus is centered in the southeast, up against the important south-Swedish countryside and the Swedish-held Scania province.

Margaret of Denmark, born in March 1353 as the sixth and youngest child of Valdemar IV of Denmark and Helvig of Schleswig, had been baptized in Roskilde and in 1359 as a six-year-old engaged to the eighteen-year-old King Haakon VI of Norway, the youngest son of the Swedish-Norwegian king Magnus IV & VII.

As part of the marriage contract it is presumed that a treaty is signed that obligates King Valdemar to assist Magnus in a dispute with his second son, Eric "XII" of Sweden, who in 1356 had been hailed as king there and had been given dominion over Southern Sweden.

Margaret's marriage is thus a part of the Nordic power struggle.

There is dissatisfaction with this in some circles, and the political activist Bridget of Sweden describes the agreement in a letter to the Pope as "children playing with dolls".

The goal of the marriage for King Valdemar is regaining Scania, which since 1332 had been mortgaged to Sweden.

The marriage contract, according to contemporary chronicles, contains an agreement to give Helsingborg Castle back to Denmark, but that is not enough for Valdemar, who in June 1359 attacks with a large army across Øresund and soon occupies Scania.

The attack is ostensibly to support Magnus against Erik's death in June 1359 Erik means that the balance of power has changed and all agreements between Magnus and Valdemar are terminated, including the marriage contract between Margaret and Haakon.

This does not get Valdemar to withdraw from Scania; he instead continues his conquests on the island of Gotland in the Baltic Sea.

Members of the Swedish Council of Aristocracy, led by Bo Jonsson Grip, had arrived in the court of Mecklenburg in 1363, after having been banished from the country after a revolt against king Magnus Eriksson.

At the nobles' request, Albert of Mecklenburg launches an invasion of Sweden supported by several German dukes and counts.

Several Hanseatic cities and dukes in Northern Germany express support of the new king.

Stockholm and …

…Kalmar, with large Hanseatic populations, also welcome the intervention.

Albert is proclaimed King of Sweden and crowned on February 18, 1364.

Magnus finds refuge with his younger son in Norway, where he will retain his sovereignty over Iceland until he drowns in 1374 in a shipwreck in Bømlafjorden.

Margaret I, the daughter of Valdemar Atterdag, had found herself married off to Håkon VI of Norway in an attempt to join the two kingdoms, along with Sweden, since Håkon had kinship ties to the Swedish royal family.

The dynastic plans had called for her son, Olaf II to rule the three kingdoms, but after his early death in 1387 she took on the role herself (1387–1412).

During her lifetime (1353–1412) the three kingdoms of Denmark, Norway, and Sweden (including the Faroe Islands, as well as Iceland, Greenland, and present-day Finland) become linked under her capable rule, in what becomes known as the Kalmar Union, made official in 1397.