The impact of Luther, and, therefore the German Reformation, continued to grow from 1530 to 1545. A precarious peace was maintained by the Schmalkaldic League between these years. The north German princes remained suspicious about any papal attempt that might lead to a settlement with the princes; especially if the settlement was based on a meeting of the Church Council based in the Papacy. However, their lip-service that they might consider a re-union with Rome indicates that the princes as a body were not totally committed to Luther. The German princes were willing for a church council to meet in Germany as it would be free form papal interference. The Holy Roman Emperor, Charles V, forbade this happening. As a devout catholic he believed that any decision about the future of the Catholic Church should come from the papacy and should be upheld anywhere in the Empire.
The princes had clearly stated their intention to fight if they felt that their growing independence was threatened and this was made clear with the creation of the Schmalkaldic League. Charles could do nothing to tackle this disobedience when he was distracted with other foreign matters primarily the Turks in the south-east corner of the empire (such as in 1539 when he had to ask the princes for money to fight the Turks).
After the failure of Regensburg in 1541, Charles decided to enforce a settlement. His long-standing enemy, Francis I, had been neutralised after the Peace of Crepy. Francis himself no longer opposed the meeting of a church council and this lead to the Council of Trent in 1545. The pope offered Charles large financial inducements to take on the "heretics" and Charles was in the difficult position of knowing that if he delayed an attack on the princes they might get themselves into a position whereby their defences were so much better than he could cope with. His other problem was not knowing if the Electors - already three in total - might in the near future become a majority of Lutherans so that any future Emperor would not be catholic. In July 1546, Charles felt strong enough to impose the ban of the Empire on John Frederick of Saxony and Philip of Hesse.
In 1547 the Schmalkaldic War broke out. Charles did not openly declare war on the "heretical" princes as this would provoke all the German princes into uniting against him. His difficult task was to be seen to be attacking heresy and not independence. He called on the princes to help him restore order and calm within the empire. In an attempt to split the princes, Charles adopted the policy of rewarding loyal princes with titles. The Saxon title was offered to a duke in Saxony called Maurice and the title would be his at the end of a victorious campaign.
The Protestant princes themselves were far from united and as a result of their lack of unity they were defeated at the Battle of Muhlburg. He ordered that the disloyal princes should gather at Augsburg but the results of this meeting were simply ignored by the princes. Charles had won a military victory but could not enforce his decisions or authority within northern Germany.
Also the victory at Mulburg proved to be self-defeating. Charles had demonstrated the menace of imperial authority over the princes. John Frederick of Saxony had most of his land confiscated and Philip was imprisoned. This treatment of two senior princes gravely angered other princes. This was a classic case of someone winning a battle but loosing the war. John Frederick was an Elector. If he could be treated in such a poor manner what about the less powerful princes and state leaders? Charles had done something even more disturbing to the state leaders.
He had given Frederick’s land to Maurice - as promised in the wake of a victorious campaign. If Charles could redistribute land legally held by a prince on one occasion, would he do it to others? Even Maurice felt threatened by this as he could not guarantee that his recent land gains would not be taken away. To re-deem his name with other princes, he was the driving force behind the League of Torgau and by 1552 the princes were ready to go on the offensive.
They brought off the new French king Henry II and quickly pushed Charles out of Germany (do not forget that Charles was Holy Roman Emperor and as such was entitled to be in his empire but such was the fall in his stature). The Catholic German princes did nothing to help Charles such was their desire for princely independence. Ferdinand, the brother of Charles, was called in to negotiate with the princes and this lead to the Treaty of Passau in 1552.
Charles’ stature took a further fall when he associated himself with the Margrave of Bayreuth who was considered by other princes as nothing more than a "robber baron". Charles took this desperate act in an attempt to reinforce his position in Germany. It failed badly and showed to the princes how desperate he was.
In 1554 Charles authorised Ferdinand to make whatever concessions he considered necessary and this lead to the Religious Peace of Augsburg in 1555.
Could Charles have ever hoped to enforce his rule in Germany?was his empire too large to allow him the time necessary to devote to the Luther issue? if he felt the Turks were more of a threat did this give the Lutherans and the princes the necessary breathing space to arm and equip themselves? Did Charles simply not understand the sheer anger that existed in north Germany with regards to the Catholic Church? Could Charles have ever hoped to compensate for the social and economic advantages that Luther gave to Germany ? How could Charles control the spread of Luther once ‘it’ had got out ? He would have found it physically impossible to stop trade which is how the word spread so quickly especially with the large river network that exists in Germany.
Ferdinand was given charge of Germany and he decided to leave the princes alone. In 1556 he became Holy Roman Emperor after his brother had abdicated all titles. By 1556 Lutheranism was well established in northern Germany and free from imperial threat - just 39 years after the 95 Theses.