The War of Unification in the South, and the formation of the Kingdom of Italy
While the War of Unification played a great part in the history of the Netherlands and of France, in the end the war had its greatest impact in Italy. Modena, which had been an ally to Paris for a century, had long been drifting away from the French kingdom. This was partially due to power politics: with Spain kicked out of Sicily and Milan, France was one of Modena/s last rivals to Italian hegemony. French support for the Kingdom of Naples during the War of Abruzzi was the last straw, and after 1629 Modena started looking for other allies.
But the geopolitical shift was not the only factor in Modena's move away from France. Florence remained one of the great sites of French diplomacy, with the most senior French ambassadors sent to the provinces of Modena. Without a major shift in Modenan politics it's likely that French could have retained all of Italy within her sphere of influence for decades longer. Power alone is not enough to stimulate a change: first the shift in power must be percieved, which means a shift in perspectives and politics. Modena's shift away from France would not have occurred without the return of the Medici family to Italian politics.
A family painting of Governor Cosimo II de Medici, along with his wife Maria Maddalena and their eldest son, Ferdinando
The Medici had been the ruling family of Florence through most of the 15th century, using the wealth derived from the Medici bank to fund massive artistic and architectural projects, as well as buying off several competing families. They were deposed during the 1493 coup, which formed the Republic of Florence, and when the Republic of Florence formed one of the founding states of the Italian League the Medici were exiled from Italy. Over the 16th century the Medici expanded their bank and became one of the major financiers of the Hapbsurg Empire, rivaling the Fuggers for influence and power. It was only in 1623 that the Medici were allowed back into Italy, a part of the Despotate's moves towards the Hapsburg Empire.
In 1635, Cosimo II de Medici was a minor magistrate in the Modenan bureaucracy. He made a name for himself when he arranged a deal with the Holy Roman Emperor Francis IV to split Milan and Venice between Modena and Austria. The Italian Wars, between the Spanish Hapsburgs, their northern Italian allies and the Austrian Hapsburgs and Modena, began the split between the Hapsburg families and Spain's decline as a major power. It also reignited Modenan desires for unification. The Unita Faction, which had been forced underground when the Modenan Duchy took over the Italian League, resurged with a vengence, demanding the destruction of the Modenan bureaucracy and the formation of a republic which would expand over all of northern Italy. This faction found its hero in the form of Cosimo, who had resigned his position in the bureaucracy to lead Modena's forces in the Italian Wars.
Modena's borders in 1643. Note that Ancona had been integrated into the Modenan Despotate, and that the French Free County of Parma was now totally isolated
General Cosimo de Medici spent the next four years building support for himself within the Italian Senate (the only thing approximating a central government in Italy), the army, and in the Modenan people. He found that he had the most loyal followers in the newly conquered territories of Milan, Verona, Sardinia, and Apulia. While he also had formed a substantial following in Florence and Siena, they tended to be pure republicans rather than supporters of a personal dictatorship or even a monarchy which Cosimo desired. Beyond building support, Cosimo built greater and greater links with the Holy Roman Empire, gaining Italian trading rights over the Adriatic and free movement between Verona and Venice.
In 1648 Cosimo came to Vienna with a contentious proposition: the Italian crown in exchange for Italian friendship. This suggestion came up against multiple problems. Firstly and foremostly, recreating the Italian Kingdom would put the Holy Roman Empire in direct conflict with the Papacy. Secondly, the title of the Kingdom of Italy had not existed for nearly six centuries, and forming a new kingdom within the Empire might legitize Bavarian, Prussian, and Saxon-Thuringian desires for their own crowns. Lastly, such a move would likely further incense the Spanish Regency Council, which was already orienting towards France.
Inspired by Henri II's massive program of artistic patronage, Cosimo established himself as one of the major patrons of Italian high baroque art. These paintings, which combined the classical subjects of French neo-classicalism and the detail of earlier baroque paintings, formed the beginning of the artistic consensus of the later 17th century, a consensus which would evolve into Rococo art
In the end it took a massive bribe for Francis IV to agree to the eventual reformation of the Kingdom of Italy. Using his links in the Medici Bank and several favors with other members of the Medici family, Cosimo II was able to arrange a loan of four million ducats to support the Hapsburgs in their war against the Ottoman Empire. With Hapsburg support gained, Cosimo traveled to Sardinia, where he petitioned the Sardinian senate to resurrect the Sardinian crown and bestow it upon him. This once again required a substantial moving of funds (this time to build a major port in the Sardinian capitol of Cagilari), but with that done, Cosimo had a royal title, and traveled back to Italy to begin his insurrection against the Modenan bureaucracy.
The Italian Royal War was short; over two thirds of the army defected to Cosimo's side and he was supported by militias from the peripheral provinces. The major section of the war was spent in protracted seiges against the loyalist cities (particularly Bologne, Modena, and Pisa)and in a desperate guerrilla warfare in the countryside. Fortunately for Cosimo, the majority of the Italian elite seige corps had defected to him and so he was able to break the the loyalist forces after two years of civil war. And so, in 1650, soon after the French defeat at Luxembourg, Cosimo was crowned Cosimo I, King of Sardinia and lord of all the Modenan lands.
Cosimo I de Medici's first royal portrait, depicting him as ruler of the world (the globe in his hand) and as a fierce warrior (with his sword prominently displayed)
This was not enough. With the French distracted and weakened, Cosimo knew he now had a chance to make a move towards attaining the crown of all of northern Italy, a chance he could not help but take. Savoy, Parma, and the Papacy were all allied with France, and Cosimo announced his acceptance of the Dutch call to arms with a simueltaneous attack against all three states. The weakened armies of the combined free Italian states could barely stand against the combined might of the Kingdom of Sardinia, especially given the outdated fortresses guarding Torino and Parma. Parma fell in the fall of 1651, and a short winter allowed the forces of Cosimo to take Torino and Roma in the spring of 1652. Each would be annexed, though the Papacy would be allowed to administer a small section of Rome as the 'Vatican City' as per Cosimo's agreement with the Austrian Hapsburgs. And so in the late spring of 1652, and at the beginning of the Fronde, Cosimo moved his forces across the Alps into southern France.
The Campaign in Southern France. Darker colors indicate earlier points of occupation, dashed lines indicate partially occupied areas at the end of the war
Cosimo focused first on the County of Savoie, in the French Alps. After the province (which was lightly fortified and barely garissoned) fell, he moved into southern France in force, focusing on taking land and ignoring the dispersed French fortresses. As such, he made steady progress over the next two years, slowly taking ports on the Rhone and laying seige to Nice, Marseilles, and Toulon at his leisure. While complications lengthened the seige of Nice, by 1655, in the middle of the Fronde, Cosimo was at the gates of Lyon and Montpellier, and advancing towards Toulouse. With his forces starting to come into conflict with the Frondeurs, Cosimo successfully sued for a peace wherein the French accepted the loss of Savoie and the annexations of Savoy, Parma, and Lazio. With this done, Cosimo began purging his own ranks of republicans and started on the hard process of subjugating the long decentralized Italian provinces under his absolute rule. The brutal unification of Italy would have major repucussions over the next century.
The Kingdom of Italy in 1660. Note that Corsica isn't in the picture but is controlled by Italy, it's apparently really hard to get quality maps of pre-unification Italy