The Reformation (1523–37)
During the 14th to 16th centuries, Denmark, Sweden and Norway were united into a series of personal unions, called the Kalmar Union (Kalmarunionen), under a single monarch. The three countries were to be treated as equals in the union. Thus, much of the next 125 years of Scandinavian history revolves around this union, with Sweden breaking off and being re-conquered repeatedly until the Regent of Sweden, Gustav Vasa, conquered the city of Stockholm and elected king of Sweden by the Swedish nobility on June 17, 1523. After crowned the King of Sweden, Gustav embraced Lutheranism and slowly broke contacts with the Papacy. Gustav suppressed aristocratic opposition to his ecclesiastical policies and efforts at centralization.
Gustav's contemporary, Christian III of Denmark, also embraced Lutheranism, resulting to a civil war in Denmark until 1536. In 1536, Denmark became officially Lutheran and established the Danish National Church (Danish: Folkekirken) as the state church. Opposition against the Reformation also occurred in Norway as the local clergy fought back against Christian III. All church valuables, including the land owned by the church, were transferred to the respective monarchs of Sweden and Denmark. After the failed rebellion, Norway was demoted from an independent kingdom to a puppet state by Christian. Scandinavia soon became one of the heartlands of Lutheranism. Catholicism almost completely vanished in Scandinavia, except for a small population in Denmark.
Dano-Swedish rivalry (1537–1818)
On August 29, 1596, Prince Christian was crowned as King Christian IV of Denmark, eight years after the death of his father King Frederick II. During his early reign, Denmark–Norway had a reputation as a relatively powerful kingdom at this time. The kingdom grew wealthy because of the increased traffic through the Øresund. Under his long reign (1588–1648), Christian IV has become known as "the architect on the Danish throne" because of the large number of building projects he undertook. Many of the great buildings of Denmark date from his reign. During the early 17th century, Sweden gradually expanded at the eastern Baltic after the Polish–Swedish War (1600–1629) and the Ingrian War (1610–1617).
In 1611, Christian IV attacked Sweden for the supremacy of the Baltic Sea. Though Denmark soon gained the upper hand, it failed to accomplish his main objective of forcing Sweden to return to the union. The war led to no territorial changes, but Sweden was forced to pay a war indemnity of one million silver riksdaler to Denmark, an amount known as the Älvsborg ransom. In 1643, Sweden, under the command of Lennart Torstensson, suddenly invaded Denmark without declaring war. Denmark was defeated and ceded to Sweden the Norwegian provinces Jemtland, Herjedalen and Älvdalen and the Danish islands of Gotland and Øsel. Despite the defeat, the Danes remember Christian IV as one of the great kings for its wartime leadership.
Following the Torstensson War of 1643, Sweden emerged as a great power, while Denmark continued to experience defeats. Sweden was able to establish control of the Eastern bank of the Øresund, formalized in the Treaty of Roskilde (1658), and gain recognition of her southeastern dominions by the European great powers in the Treaty of Oliva (1660); but Sweden was barred from further expansion at the Southern coast of the Baltic. Sweden came out of the Scanian War with only minor losses largely due to France forcing Sweden's adversaries into the treaties of Fontainebleau (1679) (confirmed at Lund) and Saint-Germain (1679).
The Enlightenment (1766–94)
Napoleonic Era (1794–1815)
On June 6, 1809, King Gustav IV Adolf of Sweden was toppled by a coup led by Lieutenant-Colonel Georg Adlersparre. The new king Charles XIII accepted the new, liberal Constitution, which was ratified by the Riksdag of the Estates the same day. Charles was childless, so in order to secure the succession to the throne, someone had to be adopted as his heir. With Adlersparre's interference, Frederick VI of Denmark was elected the heir. When Charles XIII died in 1818, Frederick was elected by the Riksdag to the throne and became King Frederick II of Sweden. Under Frederick, Denmark-Norway and Sweden were brought again into a personal union.
After the Second War of Schleswig in 1864, Denmark was forced to cede Schleswig and Holstein to Prussia following the Peace of Prague. In 1865, Denmark, Sweden and Norway signed the Treaty of Stockholm that established a union called the United Kingdom of Scandinavia with Christian IX of Denmark was elected "King of Denmark, Sweden and Norway, the Wends and the Goths, Duke of Schleswig, Holstein, Stormarn, Dithmarschen, Lauenburg and Oldenburg" with regnal name Christian I.
Started from late decades of 18th century, simple men with little education replaced professors and professionals in positions of power in Scandinavia. The peasants, in coalition with liberal and radical elements from the cities, eventually won a majority of seats in the Folketing. In 1890, King Christian I asked Arvid Posse, a member of Landsting from Left Venstre Party, to form a government. This began a tradition of parliamentary government, and no government since 1890 has ruled against a majority in the Parliament.
World War I (1914–18)
Scandinavia mostly remained neutral at the start of World War I. However, the government of Enevold Sørensen finally declared war against Central Powers in 1917. After the defeat of Germany, Scandinavia retaken the region of Northern Schleswig from Germany. The reunion day (Genforeningsdag) is celebrated every June 15 on Valdemarsdag. Scandinavia also participated in the Allied intervention in the Baltic countries against the Soviet Red Army during the Russian Civil War.
Interbellum era (1918–40)In 1920, the Agrarians emerged as a main conservative force in Scandinavia, enabled them to form a majority government with Arvid Lindman as prime minister. Lindman's government attempted to recover and revitalize country's economy that hardly challenged by the economic crisis brought on by the war. With supports from the Social Democrats and the Radical Liberals, the universal suffrage was introduced in Scandinavia in 1921. Despite Lindman's successful social and economic reforms, the Social Democrats able to form a minority government in 1924 with the Radicals with Hjalmar Branting as the country's first Social Democratic prime minister.
After 1924 election, the Agrarians and the Social Democrats emerged as two main political forces in Scandinavia, while the Radicals usually acted as a third party, shifted themselves in coalition with both sides. Most of Scandinavian conservatives, mainly from the Højre and the Old Venstre, were rallied behind the Agrarians. On other side, the Social Democrats was able to transform itself from a class-based party into a popular party, despite an earlier split by the Scandinavian Communist Party.Following the wake of Great Depression in Scandinavia, the Social Democrats gloriously won the 1929 election and able to form the first Social Democrat majority government with Thorvald Stauning as its prime minister. Under Stauning, Scandinavia developed a social welfare state for the first time. Stauning also formed a major political compromise with the Agrarians and the Radicals, that would last until 1940 and brought political stability in Scandinavia at the wake of political radicalism in Europe.
Traumatized by the nightmare of World War I, Scandinavia proclaimed itself as a neutral country in 1934. Scandinavia recognized and established the commercial relations and economic cooperation with the Union of Soviet Socialist Republics in 1936, as well as signed a 10-year non-aggression pact with Nazi Germany in 1939. However, despite declared neutral, Scandinavia formed a military alliance with Finland and Estonia known as "Northern Entente", in 1937.
World War II (1940–45)
After Germany's invasion of Poland and Czechoslovakia in 1939, World War II broke out in Europe. Amid being neutral, Scandinavia faced a danger of invasion since it was wanted to be included into the Greater Germanic Reich by the Nazis. The Scandinavian government was pressured by the United Kingdom and France to re-arm and to impose the iron ore embargo against Germany. The embargo was issued in February 1940, resulted to the German invasion to Scandinavia in April 1940.The Scandinavian government and army were not prepared for the German surprise attack. Greater Copenhagen was easily captured after a few hours, although the military and naval resistance lasted for two months. The armed forces in the north launched offensive against the German forces in the Battles of Narvik, until they were forced to surrender on June 10 after losing British help diverted to France during the Germany's invasion of France. Elements of Scandinavian government led by John Christmas Møller fled to London, while King Christian II remained in Copenhagen throughout the occupation.
In exile, the Free Scandinavian forces were formed, consists of the soldiers and officers deployed outside Scandinavia or who had fled with Møller. Through the BBC Radio service, Møller regularly spoke out against the occupation and encouraged sabotage and other resistance activities. During the occupation, Scandinavian resistance movement fought the German occupation forces with both civil disobedience and armed resistance including the destruction of Norsk Hydro's heavy water plant and stockpile of heavy water at Vemork, which crippled the German nuclear program.