Rise to power
The deposed King Charles Canutesson had been in exile in Danzig since 1457. In the early 1460s, rumours about Charles' imminent return caused Christian I to attempt to increase his political control over Sweden.
In 1463, Archbishop Jöns Bengtsson Oxenstierna, who had been governing Sweden during King Christian's stay in Finland, was imprisoned by the King on his return and brought to Copenhagen, over the Archbishop's refusal to carry out the King's tax policies. The Archbishop's Oxenstierna and Vasa relatives, among them Kettil Karlsson, took up arms against the King, gathering a peasant militia and noble supporters. Kettil Karlsson became leader of the uprising in Östergötland and northern Småland, laying siege to the unionist-controlled royal castles. His relatives gathered their forces in the northern provinces of Västmanland, Dalecarlia and Uppland, where resistance among the farmers and miners against Christian's tax and foreign trade policies was strong. In February 1464 Kettil Karlsson was elected in Västerås as Captain general of the Swedish separatists. He briefly laid siege to Stockholm but broke off the siege on receiving news of Christian I's Danish army approaching from the south, plundering Kettil Karlsson's residence at Linköping Castle on their way.
Kettil Karlsson's separatist army won a decisive victory against King Christian's Danish unionist army on 17 April 1464 at the Battle of Haraker, north of Västerås. A subsequent attempt by the unionist Lord High Constable Ture Turesson Bielke to land troops in Västmanland was defeated by Kettil Karlsson's militia from Rekarne at Kvicksund. However, Stockholm remained in the unionists' control, and the separatists lacked a fleet to blockade Stockholm harbour. A Riksmöte called by Bishop Kettil and the separatist party recalled the exiled King Charles Canutesson, who brought a fleet and mercenary troops. The city of Stockholm was captured by the separatists, who hailed Charles Canutesson as King on 9 August 1464, but Stockholm Castle remained in the hands of Ture Turesson's unionists.
Meanwhile, Archbishop Jöns Bengtsson had been released from Danish captivity due to political pressure from the Church and abroad, reconciling with King Christian. The Archbishop's arrival in Stockholm caused a conflict between the bishops and King Charles Canutesson, which rapidly escalated into open warfare. Joining forces with Ture Turesson's garrison at Stockholm Castle, the bishops soon made King Charles' position untenable.