Kalmar Union

The Kalmar Union brought the three Scandinavian kingdoms of Denmark, Norway and Sweden, together with Finland, then part of Sweden, and Norway's Atlantic islands, under a single monarch from 1397 to 1523. It was created by Queen Margaret I of Denmark, one of the most capable rulers of medieval Europe.

Margaret was born in 1353, the daughter of King Valdemar IV of Denmark, and was married at ten to King Haakon VI of Norway. Their son Olaf inherited Denmark in 1376 and Norway in 1380, with Margaret as regent. When Olaf died in 1387, Margaret was chosen as ruler of both kingdoms. Swedish nobles, unhappy with their king, Albert of Mecklenburg, a German, invited her to intervene, and in 1389 her forces defeated and captured Albert at the Battle of Åsle. Stockholm, held by Albert's German supporters, the Victual Brothers, a band of pirates, was taken in 1398.

Margaret adopted her great-nephew, Eric of Pomerania, as heir. In June 1397, at Kalmar, in south-eastern Sweden, Eric was crowned king of all three kingdoms, before an assembly of nobles and bishops. A document, the Union Letter, set out terms for the union, though historians debate whether it was ever formally ratified. Each kingdom kept its own laws, council and administration. Margaret held real power until her death in 1412.

The union aimed to strengthen Scandinavia against the German Hanseatic League, which dominated Baltic trade, and against the German princes of the south. It also served the ambitions of the Danish crown, which was the dominant partner, and of Margaret's dynasty.

Eric ruled from 1412 to 1439. He introduced the Sound Dues in 1429, a toll on ships passing through the Øresund, which became a major source of Danish revenue for over four centuries. He fought the counts of Holstein for Schleswig and the Hanseatic League, which blockaded Scandinavia. The wars required heavy taxes, which fell hard on Sweden, where Danish and German bailiffs were unpopular. In 1434 Engelbrekt Engelbrektsson, a mine owner, led a revolt of miners and peasants in Dalarna that spread across Sweden. Engelbrekt was murdered in 1436, but Eric was deposed by the Danish and Swedish councils in 1439 and spent the rest of his life on Gotland and in Pomerania.

After Eric, Christopher of Bavaria ruled all three kingdoms from 1440 to 1448. Then Sweden chose its own king, Karl Knutsson Bonde, while Denmark and Norway chose Christian I, founder of the Oldenburg dynasty. For the rest of the fifteenth century, Sweden was ruled at times by Danish kings and at times by its own regents, especially the Sture family. Sten Sture the Elder defeated Christian I at the Battle of Brunkeberg, in Stockholm, in 1471. Christian I also pledged Orkney and Shetland to Scotland in 1468–1469 as security for his daughter's dowry.

Christian II of Denmark invaded Sweden in 1520, defeating Sten Sture the Younger, who died of wounds. After his coronation in Stockholm in November 1520, Christian had more than eighty Swedish nobles, bishops and burghers executed on charges of heresy, an event known as the Stockholm Bloodbath. It provoked a new rebellion led by the young noble Gustav Eriksson Vasa, whose father had been executed. Gustav Vasa, with help from Lübeck, drove out the Danes and was elected king of Sweden on 6 June 1523, now Sweden's National Day, ending the union. Denmark and Norway remained united as Denmark-Norway until 1814.

Our maps show the Kalmar Union on the 1400 and 1500 maps. Its largest outline, about 3.1 million square kilometres on the 1500 map, is mostly Greenland, with Sweden, Finland, Norway and Iceland making up the rest. Copenhagen, Stockholm, Oslo and Helsinki lie inside it on both maps.