In 1644, Christina was declared an adult, although the coronation was postponed because of the Torstenson War. In the Treaty of Brömsebro Denmark added the isles of Gotland and Ösel to Christina’s domain while Norway lost the districts of Jämtland and Härjedalen to her. Under Christina’s rule, Sweden, now virtually controlling the Baltic Sea, had unrestricted access to the North Sea and was no longer encircled by Denmark–Norway.
Chancellor Axel Oxenstierna soon discovered that Queen Christina’s political views differed from his own. In 1645, he sent his son, Johan Oxenstierna, to the Peace Congress in the Westphalian city of Osnabrück, to argue against peace with the Holy Roman Empire. Christina, however, wanted peace at any cost and sent her own delegate, Johan Adler Salvius.
The Peace of Westphalia was signed between May and October 1648, effectively ending the European wars of religion. Sweden received an indemnity of five million thalers, used primarily to pay its troops.
Sweden further received Western Pomerania (henceforth Swedish Pomerania), Wismar, the Archbishopric of Bremen, and the Bishopric of Verden as hereditary fiefs, thus gaining a seat and vote in the Diet of the Holy Roman Empire and in the respective diets (Kreistag) of three Imperial Circles: the Upper Saxon Circle, Lower Saxon Circle, and Lower Rhenish-Westphalian Circle; the city of Bremen was disputed.
Shortly before the conclusion of the peace settlement, Queen Christina admitted Salvius into the council, against Oxenstierna’s wishes. Salvius was no aristocrat, but Christina wanted the opposition to the aristocracy present.
In 1649, with the help of her uncle, Johann Casimir, Count Palatine of Zweibrücken-Kleeburg, Queen Christina tried to reduce the influence of Oxenstierna, when she declared her cousin Carl Gustaf of Zweibrücken-Kleeburg as her heir presumptive. Carl Gustaf was the son of Johann Casimir, Count Palatine of Zweibrücken-Kleeburg and Catherine of Sweden, the daughter of King Carl IX of Sweden and his first spouse Maria of the Palatinate-Simmern.
The following year, Queen Christina resisted demands from the other estates (clergy, burghers, and peasants) in the Riksdag of the Estates for the reduction of the number of noble landholdings that were tax-exempt. She never implemented such a policy.
Already at the age of nine Christina was impressed by the Catholic religion and the merits of celibacy. She read a biography on the virgin queen, Elizabeth I of England, with interest. Christina understood that it was expected of her to provide an heir to the Swedish throne.
Her first cousin and future successor, Carl Gustaf of Zweibrücken-Kleeburg, was infatuated with her, and they became secretly engaged before he left in 1642 to serve in the Swedish army in Germany for three years.
Christina revealed in her autobiography that she felt “an insurmountable distaste for marriage” and “for all the things that females talked about and did.” She once stated, “It takes more courage to marry than to go to war.”
As she was chiefly occupied with her studies, she slept three to four hours a night, forgot to comb her hair, donned her clothes in a hurry and wore men’s shoes for the sake of convenience. (In fact, her permanent bed-head became her trademark look in paintings.)
When Christina left Sweden, she continued to write passionate letters to her intimate friend Ebba Sparre, in which she told her that she would always love her. However, such emotional letters were relatively common at that time, and Christina would use the same style when writing to women she had never met, but whose writings she admired.