Protestant Union

It was formed on 14 May 1608 by Frederick IV, Elector Palatine in order to defend the rights, land and safety of each member.

Firstly, the Holy Roman Emperor Rudolf II and Bavarian Duke Maximilian I reestablished Catholicism in Donauwörth in 1607.

Secondly, by 1608, a majority of the Imperial Diet had decided that the renewal of the 1555 Peace of Augsburg should be conditional upon the restoration of all church land appropriated since 1552.

[1] Members of the Protestant Union included the Palatinate, Neuburg, Württemberg, Baden-Durlach, Ansbach, Bayreuth, Anhalt, Zweibrücken, Oettingen, Hesse-Kassel, Brandenburg, and the free cities of Ulm, Strasbourg, Nuremberg, Rothenburg, Windsheim, Schweinfurt, Weissenburg, Nördlingen, Schwäbisch Hall, Heilbronn, Memmingen, Kempten, Landau, Worms, Speyer, Aalen and Giengen.

It allied some Protestant states in western, central and southern Germany, and fought against the Holy Roman Emperor under the guidance of Sweden and France, which were at the same time parties to that league.

Member states of the Protestant Union (blue) in the Holy Roman Empire , c. 1610
Many Protestant rulers were not members of the Union, most notably the Elector of Saxony. Religious fragmentation in Central Europe on the eve of the Thirty Years' War in 1618.
Document establishing the Protestant Union signed 14 May 1608, now in Bavarian State Archive ( Bayerische Hauptstaatsarchiv )