Margaret succeeded in uniting the Scandinavian kingdoms of Denmark, Norway and Sweden which was an accomplishment in the history of these three countries. This tri-partite union lasted for 136 years.

Margaret was the descendent of Canute, the first Danish king of England and the daughter of King Valdemar IV.

She was married at age ten to Haakon VI of Norway. Haakon was the son of Magnus Eriksson of Sweden and Norway. Although Haakon lost the crown 1 year later, he still remained soveriegn over Norway.

Margaret was an accomplished scholar who grew up at the Norwegian court. Her son, Olaf V, was born in 1370 and her father died in 1375.

The Danes willingly accepted Olaf as their king after Haakon died in 1380 and the crown was passed onto Olaf. Margaret ruled the kingdom on Haakon's beliefs. Olaf passed away in 1387 and Margaret was declared the "Sovereign lady and ruler" of both countries.

Margaret adopted her grandson, Eric of Pomerania, to provide a male ruler in 1393. She then turned her attention toward Sweden, where angry nobles were rebelling against their king and had defeated the armies of Albert of Mecklenberg and imprisoned Albert. The Hanseatic League intervened and the rebels released Albert on the condition that he pay Margaret 60,00 marks. Albert failed to pay and Margaret gained control of Sweden and the three countries united for the first and only time under Margaret's rule when Eric was crowned in 1397. Margaret continued to rule for Eric when he came of age in 1401. Margaret was moved to consolidate her power and centralize her authority in a commanding but diplomatic way. In order to do this, she set up a network of provencial sheriffs who governed their own native territories. This system served to strengthen allegiance to the crown, rather than to a region.

This system also reformed Danish currency and built up the royal treasury through taxation and reclaimed hundreds of estates in Denmark and Sweden that had once belonged to the crown. Margaret was a resourceful stateswoman in foreign affairs and maintained her countries neutrality while recovering lost Danish territory. She was able to realize the primary goals of creating a unified kingdom and sustaining Scandinavian sovereignity in the face of continued German territorial expansion to a large extent. Although the tri-partite union ended in 1525, the union between Sweden and Norway continued for 400 years until 1814. Margaret died aboard her ship In Flensborg harbor at the age of 59.