The Dano-Swedish War from 1501 to 1512 was a military conflict between Denmark and Sweden within the Kalmar Union. The war began with a Swedish revolt against King John and the siege of Queen Christina in her castle in Danish-held Stockholm. Fighting intensified in 1509 and 1510 when the German city of Lübeck and the Hanseatic League helped Sweden to conquer Danish-held Kalmar and Borgholm. The recently established Danish Navy fought joint Hanseatic-Swedish naval forces at Nakskov and Bornholm in 1510 and 1511. In April 1512, a peace agreement was signed in Malmö.. What began the war?