Task: Question Generation
Input (English): Passage: In the course of the Lutheran Reformation numerous Imperial States had adopted the new confession, against the opposition of the ruling Catholic House of Habsburg, who recognised these conversions as a quest for increasing autonomy to the detriment of the central Imperial authority. At the 1521 Diet of Worms Emperor Charles V had Martin Luther banned and the proliferation of his writings prohibited, which in 1529 provoked the Protestation at Speyer by several Lutheran estates.  The tensions culminated to an open conflict over the Lutheran Augsburg Confession of 1530, the Apology of which, written by Philipp Melanchthon, was rejected by the Emperor. In turn several Lutheran states led by Elector John Frederick I of Saxony and Landgrave Philip I of Hesse met at the town of Schmalkalden, where they established the Schmalkaldic League in 1531. In 1544 Charles V returned to Germany from the Italian War after he had signed the Treaty of Crépy and began to forge alliances not only with Pope Paul III but also with Lutheran princes, foremost with Duke Maurice of Saxony, the Albertine cousin of Saxon Elector John Frederick I. In view of the Emperor's preparations for battle, the Schmalkaldic leaders on 4 July 1546 gathered at Ichtershausen and agreed that a preventive strike would be advisable, as long as Charles V had not concentrated a significant amount of mercenaries. The Emperor gathered an army of around 52,000 men  for his campaign, that was to start on the Danube.
Output (English): How many years after banning Martin Luther did Charles V return to Germany from the Italian War?