プロテスタント同盟
In 1619, Frederick V of the Palatinate accepted the crown of Bohemia in opposition to Holy Roman Emperor Ferdinand II. On 3 July 1620 the Protestant Union signed the Treaty of Ulm (), declaring neutrality and declining to support Frederick V. In January 1621, Ferdinand II imposed an imperial ban upon Frederick V and moved his right to elect an emperor to Maximilian. Electoral Palatinate also lost the Upper Palatinate to Bavaria. The Protestant Union met in Heilbronn in February and formally protested Ferdinand's actions. He ignored this complaint and ordered the Protestant Union to disband its army. The members of the union complied with Ferdinand's demand under the Mainz accord in May, and on 14 May 1621 it was formally dissolved.