Okay, I admit it: I want to write the Great American Novel one of these days. Except in my case, it'll be the great European novel. I'm still doing research for it, and from time to time I'll add factual bits to this page. For now, though, let me set the stage...
Thanks to a series of dynastic marriages, Charles I of Spain was on the verge of becoming the most powerful monarch that Europe had ever seen. Already he was the King of Spain; in a few years, he would become Archduke of Austria and win the election for Holy Roman Emperor as well. In geographic terms this gave him, on the European continent, nominal control over Spain, the Low Countries, Germany, Austria, and a significant chunk of eastern Europe. In addition, thanks to the discoveries of the Spanish sailors a few years back, Charles would also control most of South America. Charles' driving ambition was to unite Europe against the greatest threat it had ever faced: the Muslim Ottoman Empire.
Only two European countries of significance were not part of Charles' empire: France and England. England was a minor power at the time, but it had a new king with great plans: Henry VIII. However, since Charles' aunt, Catherine of Aragon, was married to Henry, Charles could feel, perhaps, that England was safely in his pocket.
France was another matter. It, too, had an energetic king: Francis I, filled with dreams of chivalry and a return to the glorious days of the feudal romances (King Arthur, Roland, and not a few others). Francis saw no real reason to go to war against the Ottomans (after all, they were nowhere near his borders).
The stage might have been set for a great conflict between the power of France, alone, and the power of the Empire, plus Spain supported by the wealth being provided by the silver mines in America, with England throwing its lot in with the Emperor (for all his faults, Henry was no fool and knew how to pick the winning side). The outcome would be all too easy to predict, and a Europe, united, would have been the results, with incalculable consequences for the rest of the world.
This would have happened, too, except for one, obscure German priest who was about to nail 95 topics for debate on a church door in Wittenberg...