Christian II of Denmark in the context of Frederick I of Denmark

During the Reformation, the territories ruled by the Danish-based House of Oldenburg converted from Catholicism to Lutheranism. After the break-up of the Kalmar Union in 1521/1523, these realms included the kingdoms of Denmark (with the former east Danish provinces in Skåneland) and Norway (with Iceland, Greenland and the Faroe Islands) and the Duchies of Schleswig (a Danish fief) and Holstein (a German fief), whereby Denmark also extended over today's Gotland (now part of Sweden) and Øsel in Estonia.

The Reformation reached Holstein and Denmark in the 1520s. Lutheran figures like Hans Tausen, known as the "Luther of Denmark", gained considerable support in the population and from King Christian II, and though his successor Frederick I officially condemned the reformatory ideas, he tolerated their spread. His son Christian III officially introduced Lutheranism into his possessions in 1528, and on his becoming king in 1536/1537 after the Count's War, Lutheranism became official in all of Denmark–Norway. The Catholic bishops were removed and arrested, and the church was reorganized based on Lutheran church orders drawn up under the aegis of Luther's friend Johannes Bugenhagen in 1537 (Denmark–Norway) and 1542 (Holstein).

Christina Nilsdotter Gyllenstierna of Fogelvik (Swedish: Kristina or Kerstin: 1494 – January 1559) was a Swedish noblewoman. She was married to the Swedish regent Sten Sture the Younger and led the Swedish resistance against Christian II of Denmark after the death of her spouse. In her own lifetime, she was simply referred to as Fru Kristina ('Lady Christina'), but she has become known in history as Kristina Gyllenstierna because of the noble family to which she belonged.

Jan Gossaert (c. 1478 – 1 October 1532) was a French-speaking painter from the Low Countries also known as Jan Mabuse (the name he adopted from his birthplace, Maubeuge) or Jennyn van Hennegouwe (Hainaut), as he called himself when he matriculated in the Guild of Saint Luke, at Antwerp, in 1503. He was one of the first painters of Dutch and Flemish Renaissance painting to visit Italy and Rome, which he did in 1508–09, and a leader of the style known as Romanism, which brought elements of Italian Renaissance painting to the north, sometimes with a rather awkward effect. He achieved fame across at least northern Europe, and painted religious subjects, including large altarpieces, portraits and mythological subjects.

From at least 1508 he was apparently continuously employed, or at least retained, by quasi-royal patrons, mostly members of the extended Habsburg family, heirs to the Valois Duchy of Burgundy. These were Philip of Burgundy, Adolf of Burgundy, Christian II of Denmark when in exile, and Mencía de Mendoza, Countess of Nassau, third wife of Henry III of Nassau-Breda.

The Count's Feud (Danish: Grevens Fejde), sometimes referred to as the Count's War, was a Danish war of succession occurring from 1534 to 1536, which gave rise to the Reformation in Denmark. In the broader international context, it was a part of the European wars of religion. The Count's Feud derives its name from the Protestant count, Christopher of Oldenburg, who championed the claim to the throne of the deposed catholic king, Christian II (who was forced from power in 1523), rejecting Christian III's election. Christian III was a devoted protestant who had already established Lutheranism as the state religion in Schleswig and Holstein by 1528.

The Swedish War of Liberation (1521–1523; Swedish: Befrielsekriget, lit. 'The Liberation War'), also known as Gustav Vasa's Rebellion and the Swedish War of Secession, was a significant historical event in Sweden. Gustav Vasa, a nobleman, led a rebellion and civil war against King Christian II. The war resulted in the deposition of King Christian II from the throne of Sweden, effectively ending the Kalmar Union that had united Sweden, Norway, and Denmark.
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The Stockholm Bloodbath (Swedish: Stockholms blodbad) was a trial that led to a series of executions in Stockholm between 7 and 9 November 1520. The event is also known as the Stockholm massacre. The events occurred after the coronation of Christian II as the new king of Sweden, when guests in the crowning party were invited to a meeting at Tre Kronor castle. Archbishop Gustav Trolle, demanding economic compensation for things such as the demolition of Almarestäket's fortress, questioned whether the former Swedish regent Sten Sture the Younger and his supporters had been guilty of heresy.

Supported by canon law, nearly 100 people were executed in the days following the meeting despite promises of amnesty. Among those killed were many people from the aristocracy who had been supporting the Sture party in the previous years. Thereafter King Christian II became known in Sweden as Kristian Tyrann ("Christian [the] Tyrant").