Shortly thereafter, Maurice, the Duke (and later, Elector) of Albertine Saxony, invaded the lands of his rival and stepbrother in Ernestine Saxony, John Frederick, beginning the brief, but devastating, conflict known as the Schmalkaldic War. The military might of Maurice combined with that of Charles V proved to be overwhelming to John Frederick and the Protestant Schmalkaldic League. On 24 April 1547, the armies of the Schmalkaldic League were decisively defeated at the Battle of Mühlberg.