The War of the League of Cognac (1526–1530) was fought between the Habsburg dominions of Emperor Charles V—chiefly the Holy Roman Empire and Spain—and the League of Cognac, an alliance comprising the Kingdom of France, Pope Clement VII, the Republic of Venice, the Duchy of Milan and the Republic of Florence, later joined by the Kingdom of England. The war is best known for the Sack of Rome by the Emperor's unpaid troops in 1527, an event that some historians regard as the end of the Italian Renaissance. France withdrew from the war under the Treaty of Cambrai in 1529, and the League's last holdout, Florence, fell in 1530. This cemented Habsburg dominance over the Italian Peninsula.
Prelude
Alarmed by the French defeat in the Italian War of 1521, Pope Clement VII and the Republic of Venice set about building an alliance to drive Charles V from the Italian Peninsula. Francis I, who had been made prisoner at Pavia, and having signed the Treaty of Madrid and left his two eldest sons in Spain as surety for its terms, was released from his captivity in Madrid. Upon is return to France, he promtply declared his intention of assisting the Pope in his endeavor. Thus, on 22 May 1526, the League of Cognac was formed in the eponymous French town by the French king, the Pope, the republics of Venice and Florence, and Francesco II Sforza, Duke of Milan, who sought to cast off the Imperial yoke. Henry VIII of England, thwarted in his desire to have the treaty signed in England, refused to join the alliance.
Initial moves
The League swiftly seized the town of Lodi, but Imperial troops marched into Lombardy and before long forced Sforza to abandon Milan. In the meantime the powerful Colonna family, seeking to exploit the Papacy's momentary weakness, mounted an attack upon Rome. In September 1526 they defeated the Papal forces and briefly held the city, withdrawing only after being paid off.
Sack of Rome
Charles V gathered a force of 14,000 German landsknecht mercenaries and 6,000 Spanish tercio soldiers led by Georg Frundsberg and the Duke of Bourbon; the two hosts combined at Piacenza and advanced towards Rome. Francesco Guicciardini, then in command of the Papal armies, proved unable to thwart their progress; when Bourbon fell in the assault, the underpaid Imperial troops mutinied and sacked the city. The Pope took refuge in the Castel Sant'Angelo, his flight made possible by the Swiss Guards' last stand.
Siege of Naples
The sack of Rome, which effectively removed the Pope from any active role in the war, prompted frantic action on the part of the French. On 30 April 1527, Henry VIII and Francis signed the Treaty of Westminster, by which they pledged to combine their forces against the Emperor. Francis, having finally drawn England into the League, dispatched an army under the Viscount of Lautrec and the Count of Oliveto southward through Genoa—where Andrea Doria had declared for the French and seized much of the Genoese fleet—to Naples, where it proceeded to dig itself in for a protracted siege.
Collapse of the French campaign
Doria, however, soon deserted the French for Charles. The siege of Naples collapsed as plague broke out in the French camp, killing the greater part of the army together with Lautrec and Oliveto. Doria then took the offensive in Genoa, where he soon broke the blockade of the city and forced the surrender of the French garrison at Savona. These reverses, together with the decisive defeat of a French relief force under the Count of Saint-Pol at Landriano, put an end to Francis's hopes of regaining his hold on Italy.
Siege of Monopoli
Between March and May 1529, Imperial forces laid siege to Monopoli, one of several ports in Apulia then held by the League of Cognac, with the aim of regaining access to the Adriatic. The Venetian defenders held firm, and eventually emerged as the effective victors; within a few months however, Monopoli was surrendered to the Spanish under the terms of the Republic's settlement with the Emperor.
Barcelona, Cambrai, and Bologna
His armies defeated, Francis sought terms with the Emperor, who had shortly before sailed from Barcelona for Italy. Negotiations began in July 1529 in the border city of Cambrai, and were conducted primarily by two women: Francis's mother, Louise of Savoy, on behalf of France, and her sister-in-law, Margaret of Austria, on behalf of her nephew the Emperor; whence the treaty came to be known as the Paix des Dames ("Peace of the Ladies"). The final terms largely mirrored those of the Treaty of Madrid three years earlier: Francis renounced his claims to Artois, Flanders, and Tournai, and was obliged to pay a ransom of two million gold écuss for the release of his sons from their captivity in Madrid. Removed, however, were both the humiliating surrender of Burgundy itself and the various points dealing with the Duke of Bourbon, whose death two years prior extinguished any prospect of his being made an independent ruler of Provence. The final Treaty of Cambrai, signed on 3 August, withdrew France from the war, leaving Venice, Florence, and the Pope alone against the Imperial forces.
Charles, having landed at Genoa, proceeded to Bologna to confer with the Pope. Clement granted absolution to those who had taken part in the sack of Rome and promised to crown Charles. In return, he received Ravenna and Cervia from Venice, which was further compelled to surrender her remaining possessions in Apulia to the Emperor in exchange for being permitted to retain the holdings she had won at Marignano. Finally, Francesco Sforza was permitted to return to Milan—Charles having abandoned his earlier design to make Alessandro de' Medici Duke, in part due to Venetian objections—upon payment of 900,000 scudi.
Fall of the Florentine Republic
The Republic of Florence alone continued to resist the Imperial forces, which were led by the Prince of Orange. In 1530 a Florentine host under Francesco Ferruccio engaged the armies of the Emperor at Gavinana, and, although the Prince of Orange himself was slain, the Imperial army won a decisive victory and the Republic capitulated ten days afterwards. The Pope subsequently installed Alessandro de' Medici as Duke of Florence, which thenceforth remained a hereditary possession of the Medici; its centuries-old republican government thus brought to an end.