Bitter rivals since the end of the Viking Age (c. 793 – 1066 CE), the nations decided to form a union, under one monarch, to combat the rising threat posed by the good burghers of the Hanseatic League. 

This union would not only transform and thrust the medieval kingdoms of Scandinavia towards modernity but would also see the rise of Sweden as a great European power. 

Some three centuries after the death of Harald Hardrada, the Scandinavians were back on the world stage!

Trade networks across Europe

Despite popular opinion to the contrary, the fall of the Western Roman Empire, in 475 CE, did not shatter trade networks across Europe. 

The Romans had built roads throughout much of Europe, which connected the far-flung provinces to the Imperial Capital. 

These networks were very much damaged during the early medieval period but, generally speaking, the post-Roman societies picked up where the Romans left off and continued to trade, barter and conduct commerce near and far. 

This process was only accelerated when the rise of Islam saw the more economically advanced Abbasid Caliphate link in to European trade networks, providing a source of coveted goods and riches from West Asia and beyond.

One of the least-known facts about people in Viking societies is that they were simply damn good at commerce. 

Initial trading entrepots in Birka (Sweden) and Hedeby soon became Europe's premier bustling centers of commerce during the 8th and into the 9th century CE. 

Following the Viking expansion, trade networks were established westward, linking the Scandinavian homeland with the British Isles, Iceland, Greenland, and as far away as Newfoundland, Canada, and eastward, utilizing the many river systems of Eastern Europe to link the Baltic region with Eastern Europe, the Russian Steppe, and the Byzantine and Islamic world.

Towards the end of the Viking Age, the trade routes that the Vikings had plied, especially in Northern Germany, Scandinavia, and the Baltic Region, were not only lucrative but began to flex their economic muscle. 

By the early 12th century CE, several small German trading towns had banded together to pool resources, fend off pirates and robbers collectively, and began to develop common trade regulations. 

This was the birth of the Hanseatic League, which, by the mid-14th century CE, encompassed over 200 communities, cities, and trading ports dotted across Northern Europe.

The Hanseatic League city of Lübeck, in Germany. Photo: Albin Olsson / Shutterstock

The Hanseatic League

Though the Hanseatic League plied the waters that the Vikings, and their later Scandinavian ancestors, plied regularly, cities and communities from Norway, Denmark, and Sweden were notably absent, with the exception of the Swedish city of Visby. 

Though the League maintained kontorer (a type of foreign trading office) in Bergen (Norway), Malmö and Falsterbrö (Sweden), and there was a strong Hanseatic trading footprint in the Danish city of Nyborg, by and large, many Scandinavian cities and communities were left out.

The mid-14th century CE saw the coming of one of Scandinavia's worst catastrophes: the bubonic plague. 

Entering Norway, via a sea route from England, in 1349 CE, it reached Sweden and Denmark a year later and decimated the population. 

Estimates range from around a third (Sweden and Denmark) to as much as two thirds population (Norway) decline in the region. 

Suddenly, the burgeoning wealth of the League, right in the kingdom of Denmark, Norway, and Sweden's backyard, forced the Scandinavian aristocracy into a decision. 

The only way, they saw, to combat the rise and pesky influence of those Hanseatic burghers was to unify the three kingdoms under a personal union.

Academics are divided over whether this really was the workings of the Scandinavian aristocracy (would aristocrats really scheme and plot given they were in three different and separate kingdoms whilst Norway saw much of its aristocracy wiped out during the worst of the recent plague) or whether this was the work of a single ruler, that sheer force of nature, Margaret I of Denmark.

Margaret's creation?

Margaret I of Denmark was the youngest daughter of Danish King Valdemar IV, born in 1353 CE. 

Like most royal girls of the era, she was quickly married off to Haakon IV of Norway and bore him a son, Olaf. 

Unfortunately, her husband's and then son's untimely deaths saw her ascend to the throne of both Denmark and Norway. 

Meanwhile, events in Sweden saw Swedish nobles turn to Margaret for help to rid them of what they saw as an incompetent king, Albert (he did try to massively reduce their landholdings and riches... should you ever ascend a royal throne, probably best not to wind up the aristocracy in this way) and she happily led troops for a revolt. 

Albert was unceremoniously kicked off the Swedish throne, and the nobles happily offered it to Margaret. She was now the sole sovereign of the three kingdoms most famous for their Viking past: Denmark, Norway, and Sweden.

With no family left, Margaret's gaze turned across the Baltic Sea to the Duchy of Pomerania, where an obscure relative, her grand-nephew, Eric, ruled. 

This historical region of Central Europe, split between what is now modern-day Poland and Germany, had been devastated by Danish and Swedish raids since the Viking era. 

Part of the Holy Roman Empire, it was still, for many living in the Danish province of Scania, seen as part of their sphere of influence.

Margaret's attention turned to propping up her dynastic legacy and making sure that the Scandinavian aristocracy supported Eric, her adopted great-nephew, as an heir. 

By 1396 CE, Margaret took a backstep to pull the strings and saw Eric assume the titles of King of Norway and was elected as the King of Sweden and Denmark. 

His coronation took place in the Swedish city of Kalmar on June 17, 1397. 

This union of the three Scandinavian kingdoms would take its name from that beautiful Baltic city. A new regional powerhouse had emerged.

The flag of the city of Kalmar. Photo: Maxim Studio / Shutterstock

The Kalmar Union

The course of Scandinavian history was to be forever changed when after the coronation of Eric in Kalmar in 1397 CE. 

Though this union would ebb and flow, and was not continuous, it lasted well into the 16th century CE. 

This union of three kingdoms would see Norway, Denmark, and Sweden join with Scania, Iceland, much of present-day Finland, and various Norwegian "colonial" possessions from the Orkneys to Shetland islands as well as Greenland. 

The domestic and foreign policies were to be decided by a single monarch, and one of the largest Scandinavian polities was created, rivaling only, one could argue, the Viking creation of the "North Sea Empire" by Sweyn Forkbeard some four centuries before.

Yet as soon as it was created, cracks started to appear. Uniting three kingdoms under one personal monarch proved to be problematic in terms of bias. 

The Swedes complained when Eric took a more aggressive military stance towards the Hanseatic League – which resulted in a loss of trade and higher taxes – but benefited Denmark. 

Norway was unhappy (not for the last time in its history) with the perceived Danocentrism of court politics far away in Copenhagen. Finally, many Danish nobles felt they were better off alone, and the two other kingdoms were an economic drain on its prosperity.

By the turn of the 16th century, the Union had descended into a bitter internal conflict between Swedish and Danish nobles, with both sides trying to assert dominance. 

A series of Swedish rebellions, including two led by a father and a son (Sten Sture the Older and Sten Sture the Younger), resulted in the Danish king, Christian II, invading Sweden in 1520 CE. 

Supporters of the rebel leader, Sten Sture the Younger, were massacred in Stockholm in what was then called a "bloodbath." This was the final nail in the coffin of the Kalmar Union.

The end of an era and its fallout

The Kalmar Union was eventually declared dead when a Swedish noble, Gustav Vasa, led a rebellion against the rule of Danish King Christian II and fought his way through Sweden, taking Kalmar on 27 May 1523 CE. 

This resulted in the end of the union, which had seen Scandinavia emerge, from its post-Viking funk, as an economic powerhouse to rival the Hanseatic League. 

Unfortunately, internal politics had hampered the Union's strategic aims and vision to eventually supplant the league. Vasa was crowned King of Sweden weeks later and, on Midsummer's Eve, strolled into Stockholm to rip up the Union and thrust Sweden into the early modern period and its rise to (regional) greatness.

With Gustav Vasa finally ridding Sweden of the pesky Danish yoke, he would go about laying the foundations of a series of economic, political, and military reforms that would see Sweden rise to Great Power status during the 16th and 17th centuries. 

Denmark, licking its wounds from being upstaged by those Swedes, still was in a personal union with Norway. In fact, the Danish Privy Council had, just before Vasa's entrance into Stockholm, declared that Norway was a "province" of Denmark. One can imagine how well this went down with the Norwegians.

What eventually manifested was that Norway became a hereditary kingdom, in a union with Denmark, only to be separated in 1814 CE following the fallout of the Napoleonic Wars. 

Norway was then given to Sweden for being on the "right" side of the war (despite it having a king who was one of Napoleon's best generals!) and only attained true independence following a referendum in 1904. 

It has been argued, by many historians, that the Kalmar Union was the death knell of an independent Norway for at least five centuries.

Newsweek has published an article on the latest findings of a Kalmar Union-era shipwreck, available to read here.

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