Ludovico Sforza had already made sure of Ferdinand’s promise to conform to the plan he had invented, when the old king, at the solicitation of Piero, suddenly drew back. Sforza found out how this change had come about, and learned that it was Piero’s influence that had overmastered his own. He could not disentangle the real motives that had promised the change, and imagined there was some secret league against himself: he attributed the changed political programme to the death of Lorenzo dei Medici. But whatever its cause might be, it was evidently prejudicial to his own interests: Florence, Milan’s old ally, was abandoning her for Naples. He resolved to throw a counter weight into the scales; so, betraying to Alexander the policy of Piero and Ferdinand, he proposed to form a defensive and offensive alliance with him and admit the republic of Venice; Duke Hercules III of Ferrara was also to be summoned to pronounce for one or other of the two leagues. Alexander VI, wounded by Ferdinand’s treatment of himself, accepted Ludovico Sforza’s proposition, and an Act of Confederation was signed on the 22nd of April, 1493, by which the new allies pledged themselves to set on foot for the maintenance of the public peace an army of 20,000 horse and 6,000 infantry. Ferdinand was frightened when he beheld the formation of this league; but he thought he could neutralise its effects by depriving Ludovico Sforza of his regency, which he had already kept beyond the proper time, though as yet he was not strictly an usurper. Although the young Galeazzo, his nephew, had reached the age of two-and-twenty, Ludovico Sforza none the less continued regent. Now Ferdinand definitely proposed to the Duke of Milan that he should resign the sovereign power into the hands of his nephew, on pain of being declared an usurper. This was a bold stroke; but there was a risk of inciting Ludovico Sforza to start one of those political plots that he was so familiar with, never recoiling from any situation, however dangerous it might be. This was exactly what happened: Sforza, uneasy about his duchy, resolved to threaten Ferdinand’s kingdom. Nothing could be easier: he knew the warlike nations of Charles VIII, and the pretensions of the house of France to the kingdom of Naples. He sent two ambassadors to invite the young king to claim the rights of Anjou usurped by Aragon; and with a view to reconciling Charles to so distant and hazardous an expedition, offered him a free and friendly passage through his own States.