Ludovico Sforza, the Duke of Milan, seeking an ally against the Republic of Venice, encouraged Charles VIII of France to invade Italy, using the Angevin claim to the throne of Naples, then under Aragonese control, as a pretext. When Ferdinand I of Naples died in 1494, Charles invaded the peninsula. For several months, French forces moved through Italy virtually unopposed, since the "condottieri" armies of the Italian city-states were unable to resist them. Their sack of Naples finally provoked a reaction, however, and the League of Venice was formed against them. Italian troops defeated the French at the Battle of Fornovo, forcing Charles to withdraw to France. Ludovico, having betrayed the French at Fornovo, retained his throne until 1499, when Charles's successor, Louis XII of France, invaded Lombardy and seized Milan.