 He directed the use of the "Vernacular Liturgy" drawn up by Luther.In 1531 he formed the Schmalkaldic League with a number of other ruling princes for the continuation of the "Protestant doctrine" and for a joint defence against the Habsburg Emperor Charles V, a fierce opponent of the Reformation.John was followed in 1532 by his son, John Frederick the Magnanimous (died 1554), who was also one of the leaders of the Schmalkaldic League.