Charles V spent his reign trying to maintain the integrity of the Holy Roman Empire against the many forces that sought to undermine it. An emerging Protestantism proved to be one of the biggest internal threats. Although the papacy lent Charles V military and fiscal aid in the fight against the Protestants, it was occasionally a thorn in the emperor’s side, particularly when it was allied with Charles’s longtime nemesis, King Francis I of France. The biggest external menace to Europe came from the Ottoman Empire, which applied pressure from the east for much of Charles’s rule.