June 6 In Swedish History:
1523: The day Gustav Vasa was elected Sweden's King; 1654, Queen Kristina abdicates; 1809, new constitution and government proclamation.
(More on June 6, Nationaldagen)

June 6, 1523
The 27-year-old nobleman and insurgent Gustav Eriksson (Vasa) has since 1521, as leader for the Swedish War of Liberation (Befrielsekriget) against the Danes, been Sweden’s regent. But on June 6 in 1523, he is chosen as king of Sweden during a meeting in Strängnäs. Although not all of Sweden is entirely in Swedish hands (Stockholm is recovered only on Midsummer’s Eve) the choice of Vasa as king is usually seen as the symbolic end of Sweden’s membership in the Kalmar Union, which in turn symbolizes the country’s newly found independence. In 1916, June 6 is proclaimed as “Svenska flaggans dag” (Day of the Swedish Flag), and in 1983 it becomes Sweden’s national day, in commemoration of Vasa being chosen as king of Sweden.

June 6, 1654
Queen Kristina (1626-1689) abdicates from the throne of Sweden. Difficulties with issues of taxation and governance and problematic relations with Poland had plagued her last years as a queen, and by 1651 she had proposed she’d abdicate, though her council told her to stay. She seems to have had some sort of breakdown after that, which led to the final decision to abdicate.
Her actual reasons for abdicating are still argued by historians. Kristina was Queen regnant of Sweden from 1633 and used the title Queen of Swedes, Goths and Vandals, Grand Princess of Finland, and Duchess of Ingria, Estonia, Livonia and Karelia. She was the only surviving legitimate child of King Gustav II Adolph and his wife Maria Eleonora of Brandenburg. As the heiress presumptive, at the age of 6, she succeeded her father on the throne of Sweden upon his death at the Battle of Lützen. The National Council suggested that Christina join the government when she was 16, but she asked to wait until she had turned 18, as her father had waited until then.
In 1644 she took the throne, although the coronation was postponed because of the war with Denmark. Her first major assignment was to conclude peace with that country. She did so successfully; Denmark handed over the isles of Gotland and Ösel to Sweden, whereas Norway lost the districts of Jämtland and Härjedalen, which to this day have remained Swedish. Christina was interested in theatre and ballet. She was also herself an amateur actress, and amateur theatre was very popular at court during her reign. Plays had always interested her, especially those of Pierre Corneille. Christina was unusual in her own time for choosing masculine dress, and she also had some masculine physical features. Whether she chose her attire because of a self-perception as masculine, or purely for reasons of functional convenience, is difficult to know. After her abdication she settled in Rome where she died and is buried in the St. Peter’s Basilica (she had converted to Catholicism). From 2005 to 2011 (when his grave was moved), her marble sarcophagus was positioned next to that of Pope John Paul II.

June 6, 1809The new constitution and government proclamation of 1809 was also made on June 6 - the biggest change being the abolition of the King's sovereignty in favor of a separation of powers into executive branch (the king), tax collection (the parliament), legislative (shared between king and parliament), judicial (Sweden's Supreme Court - Högsta Domstolen). The constitution was in effect until January 1, 1975 after a parliamentary decision in 1974, "government proclamation of 1974."