Under the reign of Frederick I (1523–33), Denmark remained officially Catholic. But though Frederick initially pledged to persecute Lutherans, he soon adopted a policy of protecting Lutheran preachers and reformers, of whom the most famous was Hans Tausen. During his reign, Lutheranism made significant inroads among the Danish population. Frederick's son, Christian, was openly Lutheran, which prevented his election to the throne upon his father's death. However, following his victory in the civil war that followed, in 1537 he became Christian III and began a reformation of the official state church. In Sweden (and, politically by extension, also Finland), a major Liturgical Struggle lasted twenty years. It was intended to bring the church back half-way to Catholicism similar to the measures of the Augsburg Interim in Germany.