This Week in History recalls memorable and decisive events and personalities of the past.

17th June 1397 – The Kalmar Union is formed under the rule of Margaret I of Denmark

The Nordic countries of Sweden, Iceland, Denmark and Norway share a long common history of conflict and cooperation, of cultural exchange and cultural divergence. In more recent history some of these countries even shared the same monarch. What many people may not in fact realize is that for around 150 years all of these nations were united together under one monarch in a union known as the Union of Kalmar.

In the 14th century, a trading league of city states, based around North German and Holland, formed what they called the Hanseatic League. This trade league fought piracy and boosted trade across the Baltic and North Sea, and the cities which formed the league soon became immensely wealthy and powerful.

While the league initially focused on defence and trade, their growing power soon allowed them to begin taking a more active role in the politics of the Baltic Sea and the kingdoms along its shores. With the headquarters of the league in the North German city of Lubeck, the league’s growing power soon led to clashes with the kings of Denmark, who controlled access to the Baltic.

Between 1361 and 1370, the Hansa fought a war with the Danes and the Norwegians, and after sacking the Danish cities of Copenhagen and Helsingborg, they managed to force the kings of both Denmark and Norway to pay them 15% of all profits from trade that the kings collected.

The growing power of the Hansa and the German states to the south forced the Scandinavian kingdoms to put aside their differences and unite.

Queen Margaret I of Denmark, through diplomacy and some clever marriage alliances, was able to place her great-nephew, Eric of Pomerania, on the thrones of Sweden, Denmark and Norway at the same time and acted as his regent for the first few years of his reign, and remained the power behind the throne until her death.

The three kingdoms were formally united on 17 June 1397, when at a special congress of the nobles of the three kingdoms, Eric was made king of all three nations.

The king and the nobility signed a treaty which promised ‘everlasting union’, with all three kingdoms remaining separate but existing together ‘in harmony and love’.

While Margaret led the union her skillful politicking and balancing of the nobles of the three nations against one another held the union together. But it was not to last.

When Margaret died in 1412, things began to fall apart.

The union was divided by tensions between the nobles of the three realms – particularly the Swedish nobles, who resented the power of Denmark in the union.

There was also conflict between the monarchs – who tried to use the union to cement their power – and their nobles, who wanted to protect their power and regional influence.

These internal divisions weakened the union. In 1521, a Swedish noble called Gustav Vasa began a fourth rebellion against the King.

These tensions led to numerous rebellions, particularly by the Swedish, who repeatedly elevated their own candidate to the throne of Sweden only to be defeated and to rejoin the union.

With support from the Hansa, and the support of many local Swedish nobles and peasants, Gustav was able to defeat the Danish and Norwegian armies and have himself crowned King of Sweden in 1523, bringing an end to the Union of Kalmar.

Norway and Denmark would remain unified under one monarch until 1814, when control was given to Sweden, and Norway would finally become independent in 1905 when it voted to end its union with Sweden, which you can read about in this earlier edition of This Week in History.

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