The Kalmar Union (Danish/Norwegian/Swedish: Kalmarunionen) was a series of personal unions (1397–1520) that unitied the three kingdoms of Denmark, Norway and Sweden under a single monarch. The countries had given up their sovereignty, but not their independence, and diverging interests (especially Swedish dissatisfaction over the Danish and Holsteinish dominance) gave rise to a conflict that would hamper it from the 1430s until its final dissolution in 1523.
The union was formed by Queen Margaret I of Denmark (1353–1412) in the Swedish town of Kalmar, then close to the Danish border, after Danish and Swedish troops in 1389 had defeated the Swedish king, Albert of Mecklenburg, and he subsequently failed to pay the required tribute of 60,000 silver marks within three years after his release. King Albert, born in Germany, was disliked by the Swedish nobility and their rebellion had received help from the Danes, who intended the union to serve as a check on the growing power of the German Hanseatic League. Queen Margaret, who was a daughter of the late Danish king Valdemar Atterdag and wife of the late Norwegian king Haakon VI, maneuvered to have her grandnephew Eric of Pomerania recognized as heir to the Norwegian throne, and then elected king over the two other countries. Margaret promised to protect the political influence and privileges of the nobility under the union, but Eric wanted to strengthen the monarchy.
The Swedes were not happy with the Danes' frequent wars on Schleswig, Holstein, Mecklenburg, and Pomerania, which were a disturbance to Swedish exports (notably iron) to the Continent. Furthermore, the centralization of government in Denmark raised suspicions. The Swedish Privy Council wanted to retain a fair degree of self-government. The unity of the union eroded in the 1430s, even to the point of armed rebellion, leading to the expulsion of Danish forces from Sweden. Eric was deposed (1438–1439) as the union king and was succeeded by the childless Christopher of Bavaria. In the power vacuum that arose following Christopher's death (1448), Sweden elected Charles VIII king with the intent to reestablish the union under a Swedish crown. Charles was elected king of Norway in the following year, but the counts of Holstein were more influential than the Swedes and the Norwegians together, and made the Danish Privy Council appoint Christian I of Oldenburg as king. During the next seven decades struggle for power and the wars between Sweden and Denmark would dominate the union.
After the successful retaking of Sweden by Christian II and the subsequent Stockholm bloodbath in 1520, the Swedes started yet another rebellion which ousted the Danish forces once again in 1521. While independence had been reclaimed the election of King Gustav of the Vasa on June 6, 1523, restored sovereignty for Sweden and finally dissolved the union.
The last structures of the Kalmar Union remained until 1536 when the Danish Privy Council, in the aftermath of a civil war, unilaterally declared Norway to be a Danish province, without consulting their Norwegian colleagues. As Norway was a hereditary kingdom, it was in the king's interest to maintain Norway's formal status as semi-independent, to insure that future members of the Oldenburg dynasty would be elected to the Danish throne. Norway kept some separate institutions and its legal system, but the former Norwegian possessions of Iceland, Greenland, and the Faroe Islands, came directly under the Danish crown. In 1814 the king of Denmark-Norway was forced to cede Norway to the king of Sweden. In the middle of the 19th century, this would give rise to the Scandinavian movement, which sought to reunite the countries of the Kalmar Union, except Finland, under one monarch.