 Gustavus Adolphus of Sweden was since 1626 involved in the Polish-Swedish War, with Poland allied to the Holy Roman Empire.In this war, Scotsman Alexander Leslie started his career in Swedish service as commandant and governor of Pillau in East Prussia.Gustavus Adolphus had made plans to intervene in the Holy Roman Empire, of which the Riksdag commission approved in the winter of 1627/28.