After defeating a Danish counter-attack outside Västerås, Vasa sent two of his military commanders, Jöns Olofsson and Lars Eriksson, to take control of the eastern province of Uppland.

Lars Eriksson had by then reached Enköping, where he met Bjugg, and forced his troops on a retreat to Uppsala.

The Danes had yet no clear view of the rebellion's full scope, and did not believe that Uppsala would be attacked any time soon.

The Swedish peasant army attacked on the night between the 18th and 19 May, after the mass of Eric the Saint had been celebrated in the city, catching the Danish forces by surprise.

However, he managed to rally more troops and by the time of Midsummer the same year he had pushed back the Danish governmental forces.