As the Ottomans pressed westward, Sultan Murad II destroyed the last Papal-funded Crusade at Varna on the Black Sea in 1444 and four years later crushed the last Hungarian expedition. John Hunyadi and Giovanni da Capistrano organised a 1456 Crusade to lift the Siege of Belgrade. Æneas Sylvius and John of Capistrano preached the Crusade, the princes of the Holy Roman Empire in the Diets of Ratisbon and Frankfurt promised assistance, and a league was formed between Venice, Florence and Milan, but nothing came of it. Venice was the only polity to continue to pose a significant threat to the Ottomans in the Mediterranean, but it pursued the "Crusade" mostly for its commercial interests, leading to the protracted Ottoman–Venetian Wars, which continued, with interruptions, until 1718. The end of the Crusades, in at least a nominal effort of Catholic Europe against Muslim incursion, came in the 16thcentury, when the Franco-Imperial wars assumed continental proportions. Francis I of France sought allies from all quarters, including from German Protestant princes and Muslims. Amongst these, he entered into one of the capitulations of the Ottoman Empire with Suleiman the Magnificent while making common cause with Hayreddin Barbarossa and a number of the Sultan's North African vassals.