Bohemian Wars of Religion
The election of George of Podiebrady led to dissent amongst many Catholic nations in the Empire as Podiebrady was a prominent Protestant leader in Bohemia. Podiebrady and his successors changed the state religion to Protestantism without Imperial authority, prompting tensions with neighbours particularly Austria and Poland, both of whom wished to suppress the "Protestant heretics" before their ideas spread to their lands.
The first war led to the annexation of much of Bohemia's former territory by Austria and Poland. A truce was established until Henry IV of Bavaria annexed Austrian Saalfeld leading to a second war, during which Prussia also entered the war on the Bohemian side after officially converting.
Though aided by Bavaria and Prussia, Bohemia lost more lands to the Austrians and Poland annexed all Prussian lands to the east of its main power base. Additionally, the Duchy of Schleswig-Holstein declared independence from Prussia and joined the war against it.