Gustavus Adolphus was born in Stockholm on 19 December 1594, eldest son of Duke Charles of the House of Vasa and his second wife, Christina of Holstein-Gottorp. At the time, his cousin Sigismund was both King of Sweden and Poland. The Protestant Duke Charles forced the Catholic Sigismund to let go of the throne of Sweden in 1599, a part of the preliminary religious strife before the Thirty Years' War, and reigned as regent before taking the throne as Charles IX of Sweden in 1604. Crown Prince Gustav Adolph had Gagnef-Floda in Dalecarlia as a duchy from 1610. Upon his father's death in October 1611, a sixteen-year-old Gustavus inherited the throne, being declared of age and able to reign himself at seventeen as of 16 December. He also inherited an ongoing succession of occasionally belligerent dynastic disputes with his Polish cousin. Sigismund III wanted to regain the throne of Sweden and tried to force Gustavus Adolphus to renounce the title.