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.