Her father, Gustavus Adolphus, had come to the aid of the German Protestants in the Thirty Years' War, to diminish Catholic influence and gain economic influence in the German states around the Baltic Sea. He won several battles, and in 1631, Cardinal Richelieu decided France would support Sweden with money and soldiers. But Gustavus was killed in 1632. Count Oxenstierna became regent and continued Sweden's part in the war. Defeated in the Battle of Nördlingen (1634), the Swedish army retreated from southern Germany to Pomerania. Though Sweden won some later battles, the war effort was exhausting. Christina reached her majority in 1644, and Chancellor Oxenstierna soon discovered that her political views differed from his own. In 1645 he sent his son, Johan Oxenstierna, to the Peace Congress in the Westphalian cities of Osnabrück and Münster, to argue against peace. 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, she admitted Salvius into the council, against Chancellor Oxenstierna's wishes. Salvius was no aristocrat, but Christina wanted opposition to the aristocracy present. In 1645 Christina invited Hugo Grotius to become her librarian, but he died on his way in Rostock. That same year she founded "Ordinari Post Tijdender" ("Regular Mail Times"), the oldest currently published newspaper in the world. In 1647 Johann Freinsheim was appointed as her librarian. After the Battle of Prague (1648), where her armies looted Prague Castle, many of the treasures collected by Rudolph II were brought back to Stockholm.