Excerpts from Books and Wikipedia
"Gustav Eriksson finally managed to eject the Danes from his country in 1521. In return, he was proclaimed regent and on June 6, 1523 he was elected king. On June 24, the relatively unknown King Gustav I marched into Stockholm in triumph. . . . [As] the first truly authoritative ruler of Sweden, Gustav laid the foundations for a stable, centralized Swedish state, and that by forming Sweden's first professional army. Gustav created the conditions that would enable Sweden to become a regional power in the seventeenth century. . . . The king soon came into conflict with the papacy over his intention to select his own archbishop, since Gustav Trolle, the papal choice, was thought to be a Danish sympathizer. Despite the protests of Rome, Gustav appointed Laurentius Petri, the brother of a Lutheran scholar. Gustav had therefore set in motion the events by which Sweden would adopt Protestantism." [Furtado: 1001 Days]