With the support of the pope, Christian invaded Sweden in 1519 at the head of a large mercenary army after an antiunion Swedish faction led by Sten Sture (Sture, Sten, The Younger) the Younger had imprisoned the unionist archbishop Gustav Trolle. After defeating the Sture forces and taking Stockholm (September 1520), Christian, at the instigation of Trolle, had more than 80 Swedish nobles executed for heresy on November 8 and 9. Further executions followed, spreading throughout Sweden and Finland. The Kalmar Union seemed secured, but the outrage of the bloodbath alienated virtually all Swedish factions from support of the union. By 1522 Gustav I Vasa (reigned 1523–60) was able, with the help of the peasants of the Dalarna region and the Hanseatic League, to drive the Danes out of Sweden and finally to dissolve the Kalmar Union.