The Schmalkaldic War (German: Schmalkaldischer Krieg) refers to the period of violence from 1546 until 1547 between the armies of Charles V and the Schmalkaldic League within the realms of the Holy Roman Empire. The Schmalkaldic League was a defensive alliance of Lutheran princes within the Holy Roman Empire during the mid-16th century. starting for religious reasons at the Protestant Reformation, its members eventually wanted to substitute the Holy Roman Empire as a political allegiance. It was a militarily powerful alliance to confront Charles V and defend their political and religious interests.
The war began when the Duke of Albertine Saxony, Maurice, invaded the lands of his rival and stepbrother in Ernestine Saxony, John Frederick, for political reasons. Both rulers were Protestant. John Frederick, as co-founder of the Schmalkaldic League, received the support of its allies against the Catholics, allied to Charles V. Ernestine Saxony was swiftly liberated by the army of John Frederick. He later occupied Albertine Saxony and Bohemia. Without the expected military support of the Protestants of Bohemia, Charles V forced John Frederick to retreat. Strategies divergences caused the defeat of the League's defenses on 24 April 1547, at the Battle of Mühlberg, where John Frederick was taken prisoner.
Map Source: University of Texas at Austin, Perry-Castaneda Library, Map Collection
From "The Cambridge Modern History Atlas" edited by Sir Adolphus William Ward, G.W. Prothero, Sir Stanley Mordaunt Leathes, and E.A. Benians. Cambridge University Press; London. 1912