The Schmalkaldic War refers to the short period of violence from 1546 until 1547 between the forces of Charles V and the Schmalkaldic League within the domains of the Holy Roman Empire.The war begins when Maurice, the Duke (and later, Elector) of Albertine Saxony, invades the lands of his rival and step-brother in Ernestine Saxony, John Frederick, for political reasons (both rulers are Protestant).

As John Frederick is co-founder of the Schmalkaldic League, his allies joini him in a fight against the Catholics, including Charles V, who sidei with Maurice.