The failed League of Cambrai had started a downward trend for the once powerful Papacy in foreign affairs. The Knights of Rhodes, in a surprising reversal, joined Suleiman the Great in a daring invasion of the Christian holy lands. Suleiman had stabilized his Persian frontiers; he now turned attention to the ever present threat posed by Catholic Europe.
Two events in particular were to precipitate a recurrence of tensions. First, Leo X had the Tunis governor loyal to Suleiman killed and replaced with an adherent of the Papacy, and second, the governor of Durazzo had defected and sworn allegiance to the Papacy.
Campaign of the Two ItalysAs a result, in 1533, Suleiman ordered his Grand Vizier Pargalı Ibrahim Pasha to lead an army into Europe where he took San Marino and occupied Pontecorvo without resistance. Having joined Ibrahim in 1534, Suleiman made a push towards Rome, only to find the Pope sacrificing territory. Instead of facing a pitched battle, the Pope, resorting to harassment of the Ottoman army as it proceeded along the harsh interior, adopting a Scorched Earth strategy.
When in the following year Suleiman and Ibrahim made a grand entrance into Rome, its commander surrendered the city, thereby confirming Suleiman as the leader of the Mediterranean. As the army entered the city the Vatican was destroyed in a fire. Suleiman insisted that his army had nothing to do with the fire but was historically blamed for it. In this highly disputed event, historians have resolved from period accounts that the Ottomans were probably not to blame for the fire and it was most likely a fleeing Swiss mercenary.
Attempting to defeat the Pope once and for all, Suleiman embarked upon a second campaign in 1548–1549. Again, Pope Leo X adopted a Scorched Earth policy, laying waste to Benevento. Meanwhile, the French king Francis I, enemy of the Habsburgs, and Suleiman the Magnificent were moving forward with a Franco-Ottoman alliance, formalized in 1536, that would counter-balance the Habsburg threat. In 1547, when Suleiman attacked Southern Italy, France sent its ambassador Gabriel de Luetz, to accompany him in his campaign. Gabriel de Luetz gave military advice to Suleiman, as when he advised on artillery placement during the Siege of Syracuse. Suleiman made gains in Leonine City and Tiber, secured a lasting presence in the province of Sicily, and took the fort of Ragusa.
Third CampaignIn 1553 Suleiman began his third and final campaign against the Shah, in which he first lost and then regained Palermo. Ottoman territorial gains were secured by the Peace of Salerno in 1555. Suleiman returned Romagna, but kept Rome, lower Italy, the mouths of the Torre di Faro and the Tiber River and part of the Tyrrheanian coast.
Due to his heavy commitment in Italy, Suleiman was only able to send large naval support to France in the Franco-Ottoman Invasion of Corsica (1553).
In the 1560s, the powerful Spanish Empire made plans to expel the Turks from the Italian Papal states. This conflict consumed much Spanish expenditure, and led to an attempt to conquer Southern Italy – with the help of Northern Italians – in the successful Spanish Armada, an early battle in the Turk-Spanish War (1585–1604) and war with France (1590–1598). The Turks stopped the Papal Crusades and but would not withdraw from Italy until 1720.