In 1473, with the support of Giuliano Della Rovere, later Pope Julius II, he was made cardinal by Pope Sixtus IV, whom he succeeded on 29 August 1484 as Pope Innocent VIII. Papal election The papal conclave of 1484 was rife with factions, while gangs rioted in the streets. In order to prevent the election of the Venetian Cardinal Barbo, Camerlengo of the Sacred College of Cardinals, on the evening before the election, after the cardinals had retired for the night, the Dean of the College of Cardinals, Cardinal Giuliano della Rovere, nephew of the late Pope, and Cardinal Borgia, the Vice-Chancellor, visited a number of cardinals and secured their votes with the promise of various benefices. It was claimed that Cardinal della Rovere met secretly with Cardinal Marco Barbo in order to secure him more votes to become pope if he was promised a residence, though Barbo refused in fear it would make the conclave invalid due to simony. Cardinal della Rovere then met with Borgia, who disliked Barbo and wished to block his election, with an offer to turn their votes over to Cibò, promising them benefits for doing so. Papacy Shortly after his investiture, Innocent VIII addressed a fruitless summons to Christendom to unite in a crusade against the Turks. A protracted conflict with King Ferdinand I of Naples was the principal obstacle. Ferdinand's oppressive government led in 1485 to a rebellion of the aristocracy, known as the Conspiracy of the Barons, which included Francesco Coppola and Antonello Sanseverino of Salerno and was supported by Pope Innocent VIII. Innocent excommunicated Ferdinand in 1489 and invited King Charles VIII of France to come to Italy with an army and take possession of the Kingdom of Naples, a disastrous political event for the Italian peninsula as a whole. The immediate conflict was not ended until 1494, after Innocent VIII's death. Relations with the Ottoman Empire Bayezid II ruled as Sultan of the Ottoman Empire from 1481 to 1512. His rule was contested by his brother Cem, who sought the support of the Mamluks of Egypt. Defeated by his brother's armies, Cem sought protection from the Knights of St. John in Rhodes. Prince Cem offered perpetual peace between the Ottoman Empire and Christendom. However, the sultan paid the Knights a large amount to keep Cem captive. Cem was later sent to the castle of Pierre d'Aubusson in France. Sultan Bayezid