The relations between Denmark and Sweden(; ) span a long history of interaction. The inhabitants of each speak related North Germanic languages, which have a degree of mutual intelligibility. Both countries formed part of the Kalmar Union between 1397 and 1523, but there exists an inherited cultural competition between Sweden and Denmark. From 1448 to 1790 the two kingdoms went to war against each other at nearly every opportunity; in more than one case a new king tried to prove his worth by waging war on the other country for little or no political reason. Several Dano-Swedish wars took place between 1521 and 1814.
Today, the countries are separated by the Øresund, which links the Baltic Sea and the North Sea. Denmark has an embassy in Stockholm and 2 consulates-general (in Gothenburg and Malmö). Sweden has an embassy in Copenhagen and 16 honorary consulates. Both countries are full members of the Nordic Council, of the Council of the Baltic Sea States, of the Council of Europe, Joint Expeditionary Force, European Union and NATO. Around 21,000 Swedish people live in Denmark and around 42,000 Danish people live in Sweden.
Historic conflicts
Medieval contacts and the Kalmar Union
Denmark and Sweden emerged as unified kingdoms in the context of the Christianization of Scandinavia in the 8th and 10th centuries respectively and interacted closely with one another through trade, dynastic ties and military conflicts. An early example of conflict was the conquest of Gotland in 1361. The Danish king Valdemar IV Atterdag landed with his troops on the Swedish island of Gotland and defeated a force of Gotlandic peasants. Gotland subsequently remained under Danish rule for almost 300 years—an event that was to burden relations between the two Kingdoms for a long time. Nevertheless, the Middle Ages also saw phases of largely peaceful coexistence and close dynastic interconnections, which soon paved the way for a personal union.
In 1397, the Kalmar Union was founded under Queen Margaret I, uniting the kingdoms of Denmark, Norway and Sweden under one monarch. The union also emerged as a response to pressure from the Hanseatic League and other powers in the Baltic Sea region. Although Denmark initially dominated this personal union because of its greater resources, the individual structures of the member states remained intact. Despite all differences, close cooperative relations existed in the Late Middle Ages, but these increasingly eroded during the 15th century. In Sweden, resistance arose against Danish predominance; Swedish regents such as members of the Sture family at times led the government and defended Sweden's autonomy. Repeated Union Wars followed: between 1434 and 1523 there were several uprisings and wars in which Swedish nobles fought against the Danish kings.
The tensions culminated in the early 16th century. The Danish king Christian II attempted to subjugate Sweden by force. After the capture of Stockholm in 1520, he invited the Swedish aristocracy to his coronation festivities, but broke his promise of amnesty and had around 80–90 Swedish nobles and dignitaries executed in a massacre in November 1520, the so-called Stockholm Bloodbath. This event shocked Swedish society and reignited the uprising against Danish rule. The Swedish Privy Council proclaimed the nobleman Gustav Vasa leader of the struggle for liberation. By June 1523 he had captured Stockholm and was elected king of Sweden as Gustav I. Sweden thereby left the Kalmar Union. From then on, Sweden and Denmark once again existed as separate kingdoms, and their relations changed from union to bitter rivalry over territory in the Baltic Sea region.
Rivalry and wars in the early modern period (16th–18th centuries)
The tensions erupted in the Northern Seven Years' War (1563–1570). Denmark under King Frederick II sought to restore the union, while Sweden under Eric XIV and later Johan III defended its independence. Denmark prevailed in some battles, but the large and sparsely populated Swedish realm proved impossible to conquer. In the Treaty of Stettin of 1570, Denmark finally recognized Swedish sovereignty. Sweden, for its part, had to pay a large sum to Denmark in order to recover the occupied Älvsborg Fortress (Göteborg's access to the North Sea). The fact that Sweden was able to retain the territories it had acquired in the Baltic region, especially Estonia, was a sign of its rise as a new Baltic power.
In the following decades the conflict subsided for a time, partly because Sweden was involved in other wars against Russia and Poland-Lithuania. The rivalry nevertheless persisted. At the beginning of the 17th century, Christian IV in Denmark and Gustavus Adolphus in Sweden were two ambitious monarchs whose reigns reignited the antagonism. Christian IV viewed Swedish expansion into Livonia with concern, particularly because it harmed Denmark economically, for example through a Swedish blockade of Livonian ports. In 1611, Christian IV used a dispute over trade routes in Finnmark and claims to Northern Norway as a pretext to declare war on Sweden. The Kalmar War (1611–1613), named after the city of Kalmar, which was captured by the Danes, again revealed the pattern of earlier conflicts. Denmark dominated at sea, while Sweden, despite defeats, could not be defeated on land. Christian IV managed to seize the border fortresses of Kalmar and Älvsborg, forcing Sweden to make major concessions in the Treaty of Knäred in 1613. Sweden had to renounce its claims in Northern Norway and pay the Danish crown an enormous contribution of one million rixdalers in order to regain Älvsborg. This indemnity, the so-called Älvsborg ransom, made Denmark temporarily wealthy and strengthened Christian's position to such an extent that around 1620 he was regarded as one of the financially most powerful rulers in Europe. Denmark invested the money in expanding its navy and fortresses as well as in economic projects, all with the aim of securing Danish maritime supremacy and the Sound Dues. The Sound Dues, levied from 1429 on every ship passing through the Øresund strait between Denmark and Sweden, remained an important source of revenue and at the same time a constant point of contention: they symbolized Denmark's claim to control the "gateway to the Baltic Sea", much to the annoyance of Sweden and trading nations such as the Dutch Republic.
During the Thirty Years' War (1618–1648), Sweden finally rose to the status of a great power, while Denmark lost influence after its unsuccessful intervention (1625–1629). Sweden, led by Gustavus Adolphus, won significant victories in Central Europe and brought large parts of the southern Baltic coast under its control. This Swedish predominance in turn threatened Denmark. After Sweden had also established a presence in Northern Germany toward the end of the war, it attacked Denmark directly in 1643. Field Marshal Lennart Torstensson marched into Danish Holstein with experienced troops without warning. The Torstenson War (1643–1645) became a fierce feud between the old enemies: Christian IV stubbornly defended his realm—he himself lost an eye in the naval battle off the Colberger Heide—but Denmark ultimately succumbed to Swedish superiority on land and to the support of the Dutch, allied with Sweden, at sea. In the decisive Battle of Fehmarn Belt in October 1644, the Swedes and their allies sank several Danish warships; this victory marked the beginning of the end of Danish great-power status in the Baltic Sea region. In the Treaty of Brömsebro of 1645, Sweden imposed harsh terms: Denmark had to cede the Baltic island of Gotland as well as the formerly Norwegian-Danish provinces of Jämtland and Härjedalen to Sweden. Sweden also received the Danish duchy of Halland as a pledge for 30 years and was exempted from the Sound Dues.
As Sweden under King Charles X Gustav expanded still further after the Peace of Westphalia, including into Poland and the present-day Baltic states, the Danish king Frederick III sensed an opportunity for revenge and declared war on Sweden in 1657. This move proved disastrous: Charles X reacted swiftly, invaded Jutland with an army and in the winter of 1658 accomplished a military feat by marching his troops across the frozen Danish Straits from Jutland to the gates of Copenhagen. Denmark was defenseless. Frederick III was forced to accept enormous territorial losses in the humiliating Treaty of Roskilde of February 1658. Denmark had to cede all of Scania (Skåne), Blekinge and Halland—its three eastern provinces on the Scandinavian mainland—to Sweden, as well as the Baltic island of Bornholm and the formerly Norwegian territories of Bohuslän on the west coast and Trøndelag. These cessions meant that Sweden now controlled the entire southern tip of Scandinavia, revising the strategic situation in Northern Europe in Sweden's favor. Sweden had thereby massively expanded its territory at Denmark's expense and broken traditional Danish predominance in the Baltic region.
Hardly had the ink on the treaty dried when Charles X Gustav attempted in the summer of 1658 to conquer the rest of Denmark once and for all by besieging Copenhagen. This triggered a desperate Danish defense under King Frederick III. With support from the Dutch Republic, which sought to prevent a Swedish monopoly in the Baltic Sea, Copenhagen was successfully defended. The war ended in 1660 with the Treaty of Copenhagen, which forced Sweden to withdraw. Although Denmark's main losses from the Treaty of Roskilde remained—Scania and the other eastern Danish provinces stayed Swedish—Denmark regained Bornholm and the Trøndelag region in Norway, where uprisings against the Swedes had broken out. The borders between the two realms were thereby essentially fixed as they still run today between Denmark, including Norway until 1814, and Sweden. For Denmark, however, the loss of its former core lands remained a deep trauma. The formerly Danish province of Scania was intensively "Swedified" by Sweden in the following years, but the population continued to resist the new rule for some time. Denmark, for its part, did not immediately abandon hope of recovering Scania.
King Christian V of Denmark used Sweden's weakness during the Franco-Dutch War to make another attempt to recover the lost provinces in the Scanian War. Denmark achieved several military successes in this war: the Danes were able temporarily to occupy almost all of Scania, but lost the Battle of Lund in 1676. Parts of the local population welcomed the Danes, making Swedish rule more difficult. In the end, however, the European great powers, above all France, which supported Sweden, prevented any territorial revision: in the Treaty of Lund of 1679, Sweden recovered Scania and there were no border changes. The "Skåne question", meaning the Danish desire to regain Scania, remained emotionally present in the 18th century, but receded politically. The great maritime powers did not want one power alone to control the Øresund and therefore prevented Denmark from reincorporating Scania. Sweden subsequently began to integrate the formerly Danish territories more strongly, while a distinct regional identity between the nations gradually developed in Scania.