A brief and indecisive phase in the struggle between the Roman Catholic emperor Charles V and the Protestant party within the Holy Roman Empire. The defensive League of Schmalkalden was formed in the town of that name by Protestant states in 1531. It was led by Philip of Hesse and John Frederick I of Saxony. The emperor was heavily committed elsewhere and did not come face to face with the League until 1546. Then he crushed the League with the help of Duke Maurice of Saxony, winning a notable victory at the battle of Mühlberg (24 April 1547).