The Swedes were not happy with the Danes' frequent warfare on Schleswig, Holstein, Mecklenburg, and Pomerania, which disturbed Swedish exports (notably iron) to the Continent.

In 1431 or 1432, Engelbrekt Engelbrektsson had been appointed spokesman for the people of Bergslagen to persuade King Erik to dismiss the local bailiff in Västerås, Jens Eriksen.

On April 27, 1436, a rebel army unit was sent marching towards Stockholm, where people still supported Eric due to the strong and influential Danish presence in the city.

A certain degree of inner tension among the rebelling forces occurred because the nobility and clergy decided to support Karl Knutsson Bonde, who in 1436 had risen to the position of Rikshövitsman.

In a twist of fate highly beneficial to Knutsson, Engelbrekt was assassinated on May 4 by Måns Bengtsson (Natt och Dag), the cause being an unrelated personal conflict.

Karl Knutsson Bonde gave Jens Eriksen a letter of safe passage (lejdebrev) and the bailiff returned to Sweden to visit Vadstena Abbey in December 1436.

However, as word got out of his presence, the peasantry of the nearby village of Aska broke into the monastery and brought Jens Eriksen to a local court in Motala.