The Swedes were not happy with the Danes' frequent wars on Schleswig, Holstein, Mecklenburg, and Pomerania, which were a disturbance to Swedish exports (notably iron) to the European continent.
After the briefly successful reconquest of Sweden by Christian II and the subsequent Stockholm bloodbath in 1520, the Swedes rose in another rebellion which ousted the Danish forces again in 1521, though Stockholm did not surrender until the summer of 1523.