Henry II of France had entered into a major war with the Habsburg Emperor Charles V in 1551, starting the Italian War of 1551–1559.

Seeking allies, Henry II, following the Franco-Ottoman alliance policy of his father Francis I, has sealed a treaty with Suleiman the Magnificent in order to cooperate against the Habsburgs in the Mediterranean.

The Ottomans, accompanied by the French ambassador Gabriel de Luetz d'Aramon, had already defeated a Genoese fleet under Andrea Doria in the Battle of Ponza the previous year in 1552.

A new Franco-Ottoman treaty of alliance, involving naval collaboration against the Habsburgs, had been signed on February 1, 1553, between France and the Ottoman Empire.

The Ottoman admirals Turgut and Koca Sinan, together with a French squadron under Baron Paulin de la Garde, raid the coasts of Naples, Sicily, and Elba, and Corsica.

The island of Corsica is occupied by the Genoese at this time.

The Ottoman fleet supports the French by ferrying the French troops of Parma under Marshal Paul de Thermes from Siennese Maremma to Corsica.

The French are also supported in this adventure by Corsican exiles under Sampiero Corso and Giordano Orsini (French:"Jourdan des Ursins").

The invasion of Corsica had not been explicitly approved beforehand by the French king, however.

Bastia is captured on August 24, 1553, and ...

...Paulin de la Garde arrives in front of Saint-Florent on August 26.

The Ottomans capture Bonifacio in September.

With only Calvi remaining to be captured, the Ottomans, loaded with spoils, decide to leave the blockade at the end of September, and return to Constantinople.

With the help of the Ottomans, the French had managed to take strong positions on the island and finally occupied it almost completely by the end of the summer, to the dismay of Cosimo de' Medici and the Papacy.

With the Ottoman fleet gone for the winter and the French fleet having returned to Marseilles, the occupation of Corsica is jeopardized.

Only five thousand old soldiers remain on the island, together with the Corsican insurgents.

Henry II starts negotiations with Genoa in November, but Genoa sends a force of fifteen thousand men with the fleet of Andrea Doria and begins the long recapture of the island with the siege of Saint-Florent.

An Ottoman fleet sails in the Mediterranean under Dragut but is too late, and only sails the coast of Naples before returning to Constantinople.

The French only obtain the cooperation of galliots from Algiers.

The same inactivity takes place during the siege of Bastia, which had been retaken by the Genoese.

The Turkish fleet sent to help is severely undermined by the plague and returns home towing empty ships.

The French have been cleared from most of the coastal cities by 1555 and Doria has departed, but many areas remain under French control.

Jourdan des Ursins replaces de Thermes, and is named "Gouverneur et lieutenant général du roi dans l'île de Corse".

The ambassador to the Ottoman Porte, Codignac has to go to the Ottoman headquarters in Persia, where they are waging a war against the Safavid Empire, in the Ottoman-Safavid War (1532–1555), to plead for the dispatch of a fleet.

The Turkish fleet only stands by during the siege of Calvi, and contributes little.

Gaspard de Coligny, imprisoned by Savoy in the stronghold of L'Ecluse, recovers his liberty on payment of a ransom of fifty thousand crowns.

The focus of the war has shifted to Flanders after Charles' abdication in 1556 had split the Habsburg empire between Philip II of Spain and Ferdinand I.

Gaspard de Coligny is in 1557 entrusted with the defense of Saint-Quentin against Spanish forces under the command of Duke Emmanuel Philibert of Savoy in an alliance with English troops.

The English army under the Earl of Pembroke does not arrive in time for the battle on August 10, but plays a significant role in the capture of the city that follows.

Pembroke is Mary's most effective commander at the battle of St. Quentin, leading the English contingent to victory that includes among the officers such former reformists as Lord Bray, Sir Peter Carew, Sir Nicholas Throckmorton and the surviving sons of the duke of Northumberland; Ambrose and Lord Robert Dudley.

John Dudley, the son of Northumberland, had died not long after he left the Tower and his three surviving brothers had been pardoned for their recorded treasons in January, 1555 and so duly serves the Queen and King Philip on the St. Quentin expedition, where Henry Dudley is killed and his remaining brothers win the restoration of their honor and titles.

Coligny displays great courage, resolution, and strength of character in the siege, but after the fall of the city he is captured and imprisoned.

Montmorency's attempt to relieve St. Quentin leads to his defeat and capture by Spanish Habsburg forces.

As to Philip, after the victory, 'the sight of the battlefield gave him (Philip) a permanent distaste for war' and he declines to pursue his advantage, withdrawing to the Netherlands.

The greatest impact of this battle, however, is not on France, England or Spain, but on Italy: Savoy, having won the victory, has also secured a place at the conference table when the terms of peace will be deliberated.

Another Ottoman fleet is sent to the Mediterranean in 1558 to strategically support France, but the fleet is delayed from joining a French fleet in Corsica near Bastia, possibly due to the failure of the commander Dragut to honor Suleiman's orders.

The Ottoman fleet leads the Ottoman invasion of the Balearic islands instead.

Suleiman will apologize in a letter to Henry at the end of the year 1558.

The French king, by the terms of the Treaty of Cateau-Cambrésis, agrees in 1559 to restore the duchy of Savoy and Piedmont, occupied by France since 1536, to Spain's ally, Emmanuel-Philibert of Savoy.