Many German Protestants remained neutral in the early stages of the Thirty Years' War, which began in Bohemia, then expanded after 1620 into the Palatinate.

This changed in 1629, when Emperor Ferdinand passed the Edict of Restitution, requiring any property transferred since 1552 to be returned to its original owners.

After ensuring control of the army, his next step was replacing the previous loose alliance with a more formal structure; this was driven by a perceived need to stabilise the Swedish state and doubts over the reliability of his allies.

[4] Swedish Pomerania blocked Brandenburg's own commercial ambitions in the Baltic Sea, while Saxony's ruler, Elector John George, considered Sweden as great a threat as the Imperial armies.

[5] After Lützen, John George proposed a summit of German Protestants in Dresden, to negotiate a pact of neutrality, while France suspended its subsidy payments to Sweden, and awaited developments.

Advisors urged Ferdinand to take advantage of this and reverse the 1629 Edict, but he saw a chance to recoup his losses by military means and missed the opportunity.

With the Lutheran states of Denmark-Norway and Hesse-Darmstadt acting as mediators, in November 1634, he agreed a preliminary draft with John George, known as the 'Pirnaer Noteln'.