It soon became clear that the Protestants were not just interested in spiritual matters. Some of the elite members of society saw this movement as an opportunity to increase their wealth and power by denying the authority of Rome and taking ownership of Church property. This led to the 1522 Knight's War, which Charles V was able to defeat. In 1425 this was followed by  the Peasant's Revolt, consisting again of Lutherans who now seemed to think they owed allegiance to no one. Not surprisingly for people rebelling against the authority, the uprising suffered from poor leadership and Charles V was able to suppress it as well. However, these problems of Christian unity had even more serious consequences. At this time when Christians were fighting each other, the Muslim Turks took the opportunity to launch an invasion of Christian Europe. They were led by their greatest monarch, Sultan Suleiman the Magnificant.
      The first to come under attack were the Knights of St John on the island of Rhodes. After a heroic stand against vastly superior numbers the Knights were betrayed from within and forced to retreat to Malta, which was rented to them by Charles V at a price of one falcon per year. In 1526 the Muslims marched north into Hungary, killing the Hungarian King Louis and advancing to the Austrian border. Charles V, already occupied with rebellious Protestants, was also diverted by the French invasion of Italy under King Francis I. It seemed the perfect time for France to take advantage of the situation and expand her territory, but Charles V moved south and defeated the French at Pavia in 1525, taking King Francis I prisoner. Francis signed an agreement with the Emperor who released him. The following year Charles married Isabel of Portugal, begining a long and happy marriage. However, in 1527 Francis had broken his agreement and was back in northern Italy again.
       The only troops Charles could send were poorly paid soldiers from Germany, many of whom were Lutherans. When they reached Rome the
Eternal City was sacked and pillaged. The Emperor had to go to Rome himself to bring peace to the region and at last a treaty was negotiated with the French. In 1529 the good news came in that the Muslims had been defeated at Vienna by Spanish and German forces under Count Nicholas of Austria. Charles took this opportunity to call another meeting to talk with the Protestants and reunite Christian Europe. Sadly, the result was the same and the Protestants prepared for war. The Emperor could not possibly continue to fight on all sides so he was obliged to make peace. He was then able to personally lead a counter-offensive against the Turks and won a victory at Tunis, north Africa in 1535. However, France took advantage of the situation to launch an attack on Italy and the Netherlands.
       In civilian matters, despite all of the problems of war, Charles V managed to improve the legal system in the Empire, funded Magellan's voyage to circumnavigate the globe and further explore the Americas. The Protestants soon revolted again, and again the Emperor defeated them at Muhlberg in 1547. Again hoping for reconciliation Charles tried to make peace with the Protestants and allow them to continue practises which he did not agree with, but which were also not heretical. However, Maurice of Sachsen, who was to enforce the new agreement, then declared himself to be a Protestant and formed yet another rebellion. After this, Charles decided that there was simply nothing he could do to stop the Protestant Revolution and decreed that each ruler within the Empire would decide on the religion for that area.
       Not long after this, old and exhausted, after 36 years as Holy Roman Emperor, Charles V abdicated the throne and passed the crown to his brother Ferdinand. He urged him to remain faithful to the Church and remember God in his rule of the Empire. He then retired to a monastary to spend the rest of his life in prayer and meditation. He died in 1558. Although his reign had not been happy or peaceful, he had willingly carried the cross God had chosen him to bear. He left an example of courage, loyalty and religious devotion at a time when almost everyone around him lacked them all. Without his reign it is entirely possible that Catholic Europe would have been destroyed and, beyond that, the splintered Protestant sects would likely have fallen to the conquering Turks and Christendom ceased to exist altogether.