The people of Sweden had long resented the Union of Kalmar that had united Denmark, Norway, and Sweden (which then included Finland). Throughout the 15th century, there had been sporadic attempts to break away under Swedish claimants.
The kings of Denmark held the other countries as glorified satrapies (provinces). Parts of former Swedish territory in the south were held by Denmark and Norway, while trade was in the hands of the German Hanseatic League.
Against this background, the massacre of leading Swedish nobles who belonged to the National Party (the Stockholm bloodbath of 1520) by Christian II of Denmark provoked a national reaction, and in 1523 a young nobleman called Gustav Ericcson, who took the surname Vasa, was elected king.
After a number of years of fighting, the deposition of Christian II by the Danes ultimately led to peace although for centuries Sweden was included on the Danish royal arms. In 1537, a peace between Lubeck, the leading Hanseatic power, and Sweden was arranged. As the archbishop of the Swedish church was an opponent of the new king, Gustav (1523–60) took advantage of this to establish the new Lutheran Church.
After his death, the next 50 years saw the rule successively of three of his sons. Erik XXV (1560–68) had ability but lapsed into insanity. His delusions of grandeur led to war with Denmark, Lubeck, and Poland.
By 1567, his insanity had increased to such an extent that leading men feared for their lives. He had some of the foremost nobles imprisoned; others were assassinated and one was alleged to have been murdered. He was deposed in 1568, imprisoned, and died in 1577.
His successor, John III (1568–92), was pleasant but ineffectual. He made peace with the powers at war with Sweden, and ultimately Estonia was put under Swedish control, marking the beginning of Sweden’s access to great power status.
From this time forward (ca. 1570), Sweden was considered the equal of Denmark, its great rival for the next two centuries. John vacillated between Lutheranism and Catholicism, as his wife was a Catholic, and his son was a potential heir to Poland. The son, Sigismund, adopted the Catholic faith and in 1587 became king of Poland.
Sigismund’s faith led to his deposition in the by now strongly Lutheran country, and his pronouncedly Protestant uncle, Charles II (1599–1611), took over. Thus until 1668, when the Polish Vasa line died out, there was conflict between the senior Catholic branch ruling Poland and the junior Protestant branch ruling Sweden.
Sweden’s rise to great power (1630–1723) began in the next reign, when Gustav Adolphus, Sweden’s great ruler, assumed the Crown. His first success was a treaty with Russia whereby eastern Karelia and Ingria (the area of present-day St. Petersburg) were given to Sweden so as to connect it with Estonia.
In 1630, Gustav came to the aid of German Protestants and secured a series of brilliant victories between June 1630 and his death in battle in 1632. Nevertheless, under the able chancellor of state Axel Oxensteirna, the Swedes continued their success under Queen Christina Vasa, who succeeded as a minor.
By the Treaty of Westphalia (1648) Sweden acquired large possessions in north Germany, some of which she was to hold until 1810, and part of Livonia (presentday Latvia). Christina came of age in 1644 and was brilliant, but also impulsive. Becoming interested in Catholicism, she decided to abdicate in 1654.
She then converted to Catholicism and settled in Rome, where for many years she engaged in various intrigues. Her death in 1689 marked the end of the Vasa dynasty. In 1654, her cousin, a Vasa but also a Wittelsbach and a Protestant, succeeded her as king.