Charles V's failure to control the princes was the most significant factor in the spread of Lutheranism. His failures were made apparent at diets such as Worms and Speyer where the Princes seemed to defy Charles' wishes. Although Charles showed some sense of control over the princes, this was often short-lived as he lacked the support of the Church and other influential figures. This in turn allowed the establishment of Lutheranism in Germany. .
It is commonly argued that Charles' failure to assert his power over the princes allowed Lutheranism to spread. The events which occurred at the diet of Worms in 1521 showed Charles as a weak and naive leader. Charles did not deal with Luther effectively here and instead gave him the opportunity to air his views to the Princes directly. It resulted in the diet providing a platform for Luther's ideas and from here Lutheranism expanded as many of the princes were influenced by his words including Phillip of Hesse. This became evident after Charles issued the Edict of Worms which declared Luther as a heretic and an outlaw, banned his literature and required his arrest. The Edict was seldom enforced by the Princes and their public defiance of Charles V's order suggests Charles was in no way in control of the princes. The lack of enforcement of this Edict meant people still read Luther's works and still openly supported him which allowed Lutheranism to establish itself further. .
The princes had huge successes which allowed them to gain confidence and support of other neutral princes. This consequently allowed Lutheranism to spread throughout the Holy Roman Empire as gradually more princes began implementing Lutheran ideology in their individual territory. An example of their success includes the defeat of the Peasants War at the Battle of Frakenhausen in 1525. With Charles being absent from the Empire at this time the Princes saw the opportunity to take control and their success gave them confidence and made them less controllable for Charles.