In April 1521 a twenty-one year old emperor sat in the hall at Worms and listened to a friar decline to withdraw his books. Charles V had granted Luther safe conduct under pressure from the German princes, and the day after the refusal he read the assembly a statement in his own hand: that he was descended from a long line of Christian emperors who had upheld the faith, that a single friar must be wrong if his opinion stood against the whole of Christendom, and that he would stake his lands, his friends, his body and his soul on the old religion. The Edict of Worms followed, placing Luther under the imperial ban.
It changed nothing, and the reason is the shape of the empire itself. Charles ruled a federation of princes and free cities whose rulers held real power in their own lands, and he was simultaneously at war with France, defending Hungary and Austria against the Ottomans, and governing Spain and a new empire in the Americas. Whenever he turned to Germany, another front demanded him. The princes who protected Luther were not defeated for a quarter of a century.
When the reckoning came he won it and it did not help. He crushed the Schmalkaldic League at Muhlberg in 1547 and imposed an interim religious settlement, and within five years a coalition of Protestant princes with French backing had driven him out of southern Germany and forced him to terms. The Peace of Augsburg of 1555 conceded the principle he had spent his reign resisting: that each ruler determines whether his own territory is Catholic or Lutheran, and subjects who dissent may emigrate. Religious unity in the empire was over, and it was an emperor who signed the paper.