The League of Schmalkalden Formed 27 February 1531
The League was officially established on 27 February 1531, by Philip I, Landgrave of Hesse, and John Frederick I, Elector of Saxony, the two most powerful Protestant rulers at the time. It originated as a defensive religious alliance, with the members pledging to defend each other should their territories be attacked by Charles V, the Holy Roman Emperor.
At the insistence of the Elector of Saxony, membership was conditional on agreement to the Lutheran Augsburg or Tetrapolitan Confessions. This solidified the dominance of Lutheranism in Germany .