Birger Magnusson (1280 – 1321) was hailed king when he was four years old. This was done by his father Magnus Barnlock in order to secure the succession. Birger was only ten years old when his father died, the most influential statesman being the Constable of the Realm Torgils Knutsson .

When Birger came of age there was a conflict with the Church of Sweden over interpretation of the Privileges of 1280 (the cost of the support of the Church for his father's usurpation). The Kings brothers Erik Magnusson Duke of Södermanland and Valdemar Magnusson Duke of Finland took advantage of this conflict. Torgils (Duke Valdemar's father-in-law) was executed in 1306 as a token of reconciliation between Birger and his brothers. The same year, Birger was taken captive by his brothers.

The civil war ended in the re-allotment of the Swedish provinces in 1310. Birger remained king in name, but had to give up the Royal Domain, exchanging it for eastern Uplandia, Nericia, his brother Erik's former Duchy Sudermannia, Ostrogothia, Gotland and the Castle of Viborg.

Duke Erik also held Bahusia from Norway as well as northern Hallandia and was creaing a separate kingdom centered around Göta älv. In 1317 however, Birger captured his brothers during a banquet, which lead to their death, traditionally by starvation.

Birger was ousted by his brothers' supporters in 1318 and went into exile to his brother-in-law in Denmark, taking the Royal Archives with him. His son was executed at Stockholm.

In 1320 the four year old son of Duke Erik, King Magnus VII of Norway, was halied King of Sweden (Magnus III) under the Regency of his grandmother Queen Helvig, his mother Ingeborg, daugher of Haakon V, being Regent in Norway.