Editing Thirty Years' War (section)

===Northern Italy===
{{Location map many|Northern Italy|caption = Northern Italy|border = black|width =350|float = right|relief = yes|Italy Piedmont#Italy
|label   = Montferrat    |pos = bottom|lat_deg   =45.050833|lon_deg  = 8.389722
|label2  = Turin         |pos2= left  |lat2_deg  =45|lat2_min=05|lon2_deg  = 7|lon2_min = 41
|label3  = Mantua        |pos3 = right|lat3_deg  =45|lat3_min=09|lon3_deg  =10|lon3_min = 47
|label4  = Casale        |pos4 = top|lat4_deg  =45|lat4_min=08|lon4_deg  = 8|lon4_min = 27
|label6  = Genoa         |pos6 = bottom|lat6_deg  =44.411111|lon6_deg  = 8.932778
|label5  = Milan         |pos5 = top|lat5_deg  =45|lat5_min=28|lon5_deg =9|lon5_min = 12
|label7  = Pinerolo      |pos7 = bottom   |lat7_deg  =44|lat7_min=53|lon7_deg  = 7|lon7_min = 20
}}
Northern Italy had been contested by France and the [[House of Habsburg|Habsburgs]] since the [[Italian Wars|end of the 15th century]], as its control provided access to the vulnerable southern borders of France and Austria. In addition, large sections of the [[Spanish Road]] ran through it, a route that allowed Spain to safely move recruits and supplies from their Italian possessions to support their [[Eighty Years' War|war against the Dutch]]. This reliance on long exterior lines of communication was a strategic weakness, which the French sought to exploit by disrupting the Road. This usually involved attacks on the Spanish-held Duchy of Milan, or blocking the Alpine passes.{{Sfn|Hanlon|2016|pp=118–119}}

[[Duchy of Montferrat|Montferrat]] and its fortress of [[Casale Monferrato]] were subsidiary territories of the [[Duchy of Mantua]] and their possession allowed the holder to threaten Milan. This meant when the [[Vincenzo II Gonzaga, Duke of Mantua|last duke in the direct line]] died in December 1627, France and Spain backed rival claimants, resulting in the 1628 to 1631 War of the Mantuan Succession.{{Sfn|Wedgwood|1938|pp=235–236}} The French-born [[Charles I Gonzaga, Duke of Mantua|Duke of Nevers]] was backed by France and the Republic of Venice, his rival the [[Ferrante II Gonzaga, Duke of Guastalla|Duke of Guastalla]] by Spain, Ferdinand II, Savoy and [[Grand Duchy of Tuscany|Tuscany]]. While a relatively minor conflict, the struggle had a disproportionate impact on the Thirty Years War, since [[Pope Urban VIII]] viewed Habsburg expansion in Italy as a threat to the [[Papal States]]. His opposition to Ferdinand II divided the Catholic powers, and made it acceptable for France to employ Protestant allies against Austria.{{Sfn|Wedgwood|1938|p=247}}

In March 1629, the French stormed Savoyard positions in the Pas de Suse, lifted the Spanish siege of Casale, and captured [[Pinerolo]].{{Sfn|Thion|2008|p=62}} The [[Treaty of Suza]] then ceded the two fortresses to France and allowed their troops unrestricted passage through Savoyard territory, giving them control over [[Piedmont]] and the Alpine passes into southern France.{{Sfn|Ferretti|2014|pp=12–18}} However, as soon as the main French army withdrew in late 1629, the Spanish and Savoyards besieged Casale once again. At the same time, mercenaries funded by Ferdinand II were used in a Spanish offensive which routed the main Venetian field army, and forced Nevers to abandon Mantua. By October 1630, the French position seemed so precarious their representatives agreed the Treaty of Ratisbon. It was never ratified, as Richelieu claimed he had not approved the terms.{{Sfn|Wedgwood|1938|pp=263–264}}

Several factors restored the French position in northern Italy, notably a devastating outbreak of [[1629–1631 Italian plague|plague]]; between 1629 and 1631, over 60,000 died in [[Milan]] and 46,000 in [[Venice]], with proportionate losses elsewhere.{{Sfn|Kohn|1995|p=200}} Richelieu took advantage of the diversion of Imperial resources to fund a [[Swedish intervention in the Thirty Years' War|Swedish invasion of Germany]], whose success forced the Spanish-Savoyard alliance to withdraw from Casale and sign the Treaty of Cherasco in April 1631. Nevers was confirmed as Duke of Mantua and although Richelieu's representative, Cardinal Mazarin, agreed to evacuate Pinerolo, it was later secretly returned under an agreement with [[Victor Amadeus I, Duke of Savoy]]. With the exception of the 1639 to 1642 [[Piedmontese Civil War]], this secured the French position in northern Italy for the next twenty years.{{Sfn|Ferretti|2014|p=20}}

[[File:Dankaerts-Historis-9287.tif|thumb|left|upright=1.0|Siege and capture of [[Casale Monferrato]] by French troops, 1630]]

After the outbreak of the Franco-Spanish War in 1635, Richelieu supported a renewed offensive by Victor Amadeus against Milan to tie down Spanish resources. These included an unsuccessful attack on [[Valenza]] in 1635, plus minor victories at [[Battle of Tornavento|Tornavento]] and [[Mombaldone]].{{sfn|Duffy|1995|p=125}} However, the anti-Habsburg alliance in northern Italy fell apart when first Charles of Mantua died in September 1637, then Victor Amadeus in October, whose death led to a struggle for control of the Savoyard state between his widow [[Christine of France]] and brothers, [[Thomas Francis, Prince of Carignano|Thomas]] and [[Prince Maurice of Savoy|Maurice]].{{Sfn|Wilson|2009|p=259}}

In 1639, their quarrel erupted into open warfare, with France backing Christine and Spain the two brothers, and resulted in the [[Siege of Turin (1640)|Siege of Turin]]. One of the most famous military events of the 17th century, at one stage it featured no less than three different armies besieging each other. However, revolts in Portugal and Catalonia forced the Spanish to cease operations in Italy, and the war was settled on terms favourable to Christine and France.{{sfn|Hanlon|2016|p=124}}

In 1647, a French-backed rebellion succeeded in temporarily overthrowing Spanish rule in [[Neapolitan Republic (1647)|Naples]]. The Spanish quickly crushed the insurrection and restored their rule over all of southern Italy, defeating multiple French expeditionary forces sent to back the rebels.{{Sfn|Kamen|2003|p=406}} However, it exposed the weakness of Spanish rule in Italy and the alienation of the local elites from Madrid. In 1650, the governor of Milan wrote that as well as widespread dissatisfaction in the south, the only one of the Italian states that could be relied on was the [[Duchy of Parma]].{{Sfn|Kamen|2003|p=407}}