Thirty Years' War

The 16th-century Reformation led to the Schmalkaldic War between Protestants and Catholics within the Holy Roman Empire. Fighting ended with the 1552 Peace of Passau, followed by the 1555 Peace of Augsburg, which tried to prevent a recurrence by fixing boundaries between the two faiths. Under the principle of cuius regio, eius religio, states were designated as either Lutheran, then the most usual form of Protestantism, or Catholic, based on the religion of their ruler. Other provisions protected substantial religious minorities in cities like Donauwörth, and confirmed Lutheran ownership of property taken from the Catholic Church since 1552.

However, the settlement was undermined by the expansion of Protestantism into Catholic areas post-1555, particularly Calvinism, a Protestant doctrine viewed with hostility by both Lutherans and Catholics. It also gave individual states greater freedom to pursue their own objectives, which often clashed with those of central authority or local rivals. Disputes over money and territory superseded religion, with the Protestant states of Saxony and Brandenburg competing with Denmark–Norway and Sweden for the lucrative Baltic trade.

Managing tensions was hampered by fragmented political institutions, with 300 imperial estates distributed across Germany, the Low Countries, northern Italy, and France. These ranged in size and importance from the seven Prince-electors who voted for the Holy Roman Emperor, down to Prince-bishoprics and imperial cities like Hamburg. Each also belonged to a separate regional grouping known as an Imperial Circle, which was chiefly concerned with defence, and operated independently. Above all of these was the Imperial Diet, which assembled infrequently, and focused on discussion, rather than legislation.

Since 1440, the position of emperor had been held by the House of Habsburg, the largest single landowner within the Holy Roman Empire. They directly ruled over eight million subjects and territories that included Austria, Bohemia and Hungary. The Habsburgs also controlled the Spanish Empire until 1556, when Charles V divided his possessions between different branches of the family. This bond was reinforced by frequent inter-marriage, while Spain retained territories within the Holy Roman Empire such as the Spanish Netherlands, Milan and Franche-Comté.

Though the Spanish and Austrian branches often collaborated, they did not generally coordinate their policies because the two entities were very different. Spain was a global maritime superpower, stretching from Europe to the Philippines and the Americas, while Austria was a land-based power, focused on Germany and securing its eastern border against the Ottoman Empire. Another key difference was the disparity in relative financial strength, with the Spanish Habsburgs providing large subsidies to their Austrian counterparts. The loss of these post-1640, as Spain itself struggled with the costs of a long running global war, substantially weakened the imperial position.

Prior to the Reformation, shared religion partially compensated for weak imperial institutions. After 1556, rising religious and political tensions allowed states like Lutheran Saxony and Catholic Bavaria to expand their own power, while further weakening imperial authority. This internal political struggle was exacerbated by external powers with their own strategic objectives, such as Spain, the Dutch Republic, or France, confronted by Habsburg lands on its borders to the north, south, and along the Pyrenees. Since a number of foreign rulers were also imperial princes, divisions within the empire drew in players like Christian IV of Denmark, who joined the war in 1625 as Duke of Holstein-Gottorp.

Disputes occasionally resulted in full-scale conflict like the 1583 to 1588 Cologne War, triggered when its ruler converted to Calvinism. More common were events such as the 1606 Battle of the Flags in Donauwörth, when riots broke out after the Lutheran majority blocked a Catholic religious procession. Emperor Rudolf approved intervention by the Catholic Maximilian of Bavaria. In return, he was allowed to annex the town, and, as agreed at Augsburg, the official religion changed from Lutheran to Catholic.

When the Imperial Diet opened in February 1608, both Lutherans and Calvinists sought re-confirmation of the Augsburg settlement. In return, the Habsburg heir Archduke Ferdinand required the immediate restoration of any property taken from the Catholic Church since 1555, as opposed to the previous practice whereby each case was assessed separately. By threatening all Protestants, his demand paralysed the Diet, and removed the perception of imperial neutrality.

Loss of faith in central authority meant towns and rulers began strengthening their fortifications and armies, with foreign travellers often commenting on the militarisation of Germany in this period. When Frederick IV, Elector Palatine formed the Protestant Union in 1608, Maximilian responded by setting up the Catholic League in July 1609. Both were largely vehicles for their leaders' dynastic ambitions, but when combined with the 1609 to 1614 War of the Jülich Succession, the result was to increase tensions throughout the empire. Some historians who see the war as primarily a European conflict argue that Jülich marks its beginning, with Spain and Austria backing the Catholic candidate, France and the Dutch Republic the Protestant.

What began as an internal dynastic dispute within the empire drew in external powers due to the imminent expiry of the 1609 Twelve Years' Truce, which suspended the Eighty Years' War between Spain and the Dutch Republic. Before restarting hostilities, Ambrosio Spinola, commander in the Spanish Netherlands, needed to secure the Spanish Road, an overland route connecting Habsburg possessions in Italy to Flanders. This allowed him to move troops and supplies by road, rather than sea where the Dutch navy was dominant; by 1618, the only part not controlled by Spain ran through the Electoral Palatinate.

Since Emperor Matthias had no surviving children, in July 1617 Philip III of Spain agreed to support Ferdinand II's election as king of Bohemia and Hungary. In return, Ferdinand made concessions to Spain in northern Italy and Alsace and agreed to support their offensive against the Dutch. Doing so required his election as emperor, which was not guaranteed; Maximilian of Bavaria, who opposed the increase of Spanish influence in an area he considered his own, tried to create a coalition to support his candidacy.

Another option was Frederick V, Elector Palatine, a Calvinist who in 1613 married Elizabeth of Bohemia, daughter of James I of England. When Ferdinand was elected king of Bohemia in 1617, he also gained control of its electoral vote, but his conservative Catholicism made him unpopular with the mostly Protestant Bohemian nobility, who were also concerned about the erosion of their rights. Since the seven electors previously consisted of three Protestants and four Catholics, replacing Ferdinand with Frederick would alter the religious balance, making possible the election of a Protestant emperor and the end of Habsburg predominance. These factors combined to bring about the Bohemian Revolt in May 1618.

Ferdinand once claimed he would rather see his lands destroyed than tolerate heresy within them. Less than 18 months after taking control of Styria in 1595, he had eliminated Protestantism in what had been a stronghold of the Reformation. Their war in the Netherlands meant the Spanish Habsburgs preferred to avoid antagonising Protestants elsewhere. However, while recognising the dangers of Ferdinand's fervent Catholicism, they ultimately supported his claim due to lack of alternatives.

Elected king of Bohemia in May 1617, Ferdinand reconfirmed Protestant religious freedoms, but his record in Styria led to the suspicion he was only awaiting a chance to overturn them. These concerns were heightened after a series of legal disputes over property were all decided in favour of the Catholic Church. In May 1618, Protestant nobles led by Count Thurn met in Prague Castle with Ferdinand's two Catholic representatives, Vilem Slavata and Jaroslav Borzita. In what became known as the Third Defenestration of Prague, both men were thrown out of the castle windows along with their secretary Filip Fabricius, although all three survived.

Thurn established a Protestant-dominated government in Bohemia, while unrest expanded into Silesia and the Habsburg heartlands of Lower and Upper Austria, where much of the nobility was also Protestant. Losing control of these threatened the entire Habsburg state, while in addition to its crucial electoral vote, Bohemia was one of the most prosperous areas of the Empire. Regaining control was vital for the Austrian Habsburgs, but chronic financial weakness left them dependent on Maximilian and Spain for the resources needed to achieve this.

Spanish involvement in Bohemia drew in the Dutch and their ally, France, although the strongly Catholic Louis XIII faced his own domestic Protestant rebellion and refused to support them elsewhere. Elsewhere, Charles Emmanuel I, Duke of Savoy helped Frederick fund a mercenary army under Ernst von Mansfeld, which was sent to support the Bohemian rebels. Attempts by Maximilian and John George of Saxony to broker a negotiated solution ended when Emperor Matthias died in March 1619, since many believed the loss of his authority and influence had fatally damaged the Habsburgs.

By mid-June 1619, an army led by Thurn was outside Vienna, and despite defeating Mansfeld at Sablat, Ferdinand's position continued to worsen. Gabriel Bethlen, the Calvinist Prince of Transylvania, invaded Hungary and besieged Vienna with Ottoman support, although war with Poland–Lithuania in 1620, followed by the 1623 to 1639 conflict with Persia, prevented their direct participation.

On 19 August, the Bohemian Estates rescinded Ferdinand's 1617 election as king and a week later formally offered the crown to Frederick. On 28 August, Ferdinand was elected Holy Roman Emperor, making war inevitable if Frederick accepted the Bohemian crown. Most of Frederick's advisors urged him to reject it, as did the Duke of Savoy, and his father-in-law James I.

However, he received backing from Christian of Anhalt, along with Maurice of Orange, for whom conflict in Germany was a means to divert Spanish resources from the Netherlands. The Dutch offered subsidies to Frederick and the Protestant Union, helped raise loans for Bohemia, and provided weapons and munitions. However, wider European support failed to materialise, largely due to lack of enthusiasm for removing a legally elected ruler, regardless of religion.

Although Frederick accepted the crown and entered Prague in October 1619, his support eroded over the next few months. In July 1620, the Protestant Union proclaimed its neutrality, while John George of Saxony backed Ferdinand in return for the cession of Lusatia and a guarantee of Lutheran rights in Bohemia. Maximilian of Bavaria funded a combined Imperial-Catholic League army led by Count Tilly and the Count de Bucquoy, which pacified Upper and Lower Austria and occupied western Bohemia before marching on Prague. Defeated at the Battle of White Mountain in November 1620, the Bohemian army disintegrated, and Frederick fled the country.

By abandoning Frederick, the German princes hoped to restrict the dispute to Bohemia, an objective thwarted by Maximilian's dynastic ambitions. In the October 1619 Treaty of Munich, Ferdinand transferred the Palatinate's electoral vote to Bavaria, and allowed Maximilian to annex the Upper Palatinate. Many Protestants had supported Ferdinand against Frederick because they opposed the deposition of a legally elected ruler, and now objected to his removal on the same grounds. For Catholics, it presented an opportunity to regain lands and properties lost since 1555, a combination which destabilised large parts of the Empire.

At the same time, Spain was drawn into the conflict due to the strategic importance of the Spanish Road, and its proximity to the Palatinate. When an army led by Córdoba occupied the Lower Palatinate in October 1619, James I sent English naval forces against Spanish colonies in the Americas, and threatened war if Spanish troops were not withdrawn by spring 1621. These actions were primarily designed to placate his opponents in Parliament, for whom his pro-Spanish policy was a betrayal of the Protestant cause. Spanish chief minister Count-Duke Olivares correctly interpreted them as an invitation to open negotiations, and in return for an Anglo-Spanish alliance offered to restore Frederick to his Rhineland possessions.

Since Frederick's demand for full restitution of his lands and titles was incompatible with the Treaty of Munich, hopes of a negotiated peace quickly evaporated. Despite defeat in Bohemia, Frederick still had allies including Georg Friedrich of Baden and Christian of Brunswick, while the Dutch provided military support and his father-in-law James funded an army of mercenaries under Mansfeld. However, failure to co-ordinate effectively led to defeats at Wimpfen in May 1622, after which Georg Friedrich made peace, and Höchst in June.

By November 1622, Spanish and imperial troops controlled most of the Palatinate, apart from Frankenthal, which was held by a small English garrison under Sir Horace Vere. After Höchst, Mansfeld and Christian united at Hagenau before moving towards the Netherlands. They were stopped by Córdoba at Fleurus, but the Protestant army escaped destruction, and made it to Bergen op Zoom. Frederick arrived in the Netherlands in 1622, where he lived in The Hague until his death in November 1632.

When the Imperial Diet met in February 1623, Ferdinand forced through provisions transferring Frederick's titles, lands, and electoral vote to Maximilian. He did so with support from the Catholic League, despite strong opposition from Protestant members, as well as the Spanish. The Palatinate was clearly lost, and in March Vere surrendered Frankenthal, while campaigning ended with Tilly's victory over Christian of Brunswick at Stadtlohn in August. However, Spanish and Dutch involvement was a significant step in internationalising the war, while Frederick's removal meant other Protestant princes began planning how to preserve their own rights and territories.

With Saxony dominating the Upper Saxon Circle and Brandenburg the Lower, both kreise remained neutral in the early stages. However, Frederick's deposition in 1623 united the Lutheran John George of Saxony and Calvinist George William, Elector of Brandenburg, over concerns Ferdinand intended to reclaim Catholic territories. These were strengthened in early 1625 when territories held by Protestants since 1566 were returned by Tilly to the Roman Catholic Diocese of Halberstadt.

As Duke of Holstein, Christian IV was also a member of the Lower Saxon circle, while the Danish economy relied on the Baltic trade and tolls from traffic through the Øresund. In 1621, Hamburg accepted Danish "supervision", while his son Frederick became joint-administrator of Lübeck, Bremen, and Verden, thus ensuring Danish control of the Elbe and Weser rivers.

Ferdinand had paid Albrecht von Wallenstein for his support against Frederick with estates confiscated from the Bohemian rebels, and now contracted with him to conquer the north on a similar basis. In May 1625, the Lower Saxony kreis elected Christian their military commander, although this was initially opposed by Saxony and Brandenburg, who viewed Denmark and Sweden as competitors, and wanted to avoid either becoming involved in the empire. Attempts to negotiate a peaceful solution failed as the conflict in Germany became part of the wider struggle between France and their Habsburg rivals in Spain and Austria.

In the June 1624 Treaty of Compiègne, France had agreed to subsidise the Dutch war against Spain for a minimum of three years, while in the December 1625 Treaty of The Hague, the Dutch and English agreed to finance Danish intervention in the Empire. Hoping to create a wider coalition against Ferdinand, the Dutch invited France, Sweden, Savoy, Transylvania, and the Republic of Venice to join, but it was overtaken by events. In early 1626, Cardinal Richelieu, main architect of the alliance, faced a new Huguenot rebellion at home and in the March Treaty of Monzón, France withdrew from northern Italy and the critical Valtellina Pass, re-opening the Spanish Road.

Dutch and English subsidies enabled Christian to devise an ambitious three-part campaign plan. While he led the main force down the Weser, Mansfeld would attack Wallenstein in Magdeburg, supported by forces led by Christian of Brunswick and Maurice of Hesse-Kassel. However, Mansfeld was defeated at Dessau Bridge in April, and when Maurice refused to support him, Christian of Brunswick fell back to Wolfenbüttel, where he died of disease shortly after. The Danes were comprehensively beaten at Lutter in August, and Mansfeld's army retreated south to the Ottoman Empire, where his army dissolved after his death in November.

Many of Christian's German allies, such as Hesse-Kassel, had little interest in replacing imperial domination with Danish, while few of the Dutch or English subsidies were ever paid. Charles I of England allowed Christian to recruit up to 9,000 Scottish mercenaries, but they took time to arrive, and although able to slow Wallenstein's advance, were insufficient to stop him. By the end of 1627, Wallenstein had occupied Mecklenburg, Pomerania, and Jutland, and began making plans to construct a fleet capable of challenging Danish control of the Baltic. He was supported by Spain, for whom it provided an opportunity to open another front against the Dutch.

On 13 May 1628, his deputy von Arnim besieged Stralsund, the only port with facilities large enough to build this fleet. Gustavus Adolphus responded by sending several thousand Scots to Stralsund under Alexander Leslie, who was also appointed governor. Von Arnim abandoned the siege on 4 August, but three weeks later Christian suffered another defeat at Wolgast. He began negotiations with Wallenstein, who despite his recent victories was concerned by the prospect of Swedish intervention, and thus anxious to make peace.

With Ferdinand's resources stretched by the outbreak of the War of the Mantuan Succession, Wallenstein persuaded him to agree relatively lenient terms in the June 1629 Treaty of Lübeck. These allowed Christian to retain Schleswig and Holstein in return for relinquishing Bremen and Verden, and abandoning support for the German Protestants. While Denmark kept Schleswig and Holstein until 1864, this effectively ended its period as a major power in the Baltic region.

Once again, the methods used to obtain victory explain why the war failed to end. Ferdinand's chronic financial weakness meant Wallenstein raised money by demanding ransoms from towns, while his men plundered the local territory, regardless of whether it belonged to allies or opponents.

By triggering direct French intervention, Nördlingen expanded the conflict rather than ending it. Richelieu provided the Swedes with new subsidies, hired mercenaries led by Bernard of Saxe-Weimar for an offensive in the Rhineland, and in May 1635 initiated the Franco–Spanish War (1635–1659). A few days later, the German states and Ferdinand agreed to the Peace of Prague. In return for withdrawing the Edict of Restitution, the Heilbronn and Catholic Leagues agreed to dissolve their forces, which were replaced by a single Imperial army, although Saxony and Bavaria retained control of their own forces. This is generally seen as the point when the war ceased to be a primarily inter-German religious conflict.

In March 1635, French soldiers entered the Valtellina, cutting the link between Milan and the Empire. This was followed in May by an invasion of the Spanish Netherlands, which collapsed with the loss of 17,000 men. In March 1636, France joined the Thirty Years' War as an ally of Sweden, which was increasingly reliant on French financing for its continued participation. The Spanish responded by invading northern France, causing panic in Paris before lack of supplies forced them to retreat. Elsewhere, Saxony began the year by occupying Pomerania, before defeats at Dömitz and Wittstock in October re-established Swedish predominance in northeast Germany.

Ferdinand II died in February 1637, and was succeeded by his son Ferdinand III, who faced a precarious military position. Although Matthias Gallas had forced Johan Banér, the new Swedish commander, back to the Baltic, in March 1638 Bernard of Saxe Weimar destroyed an Imperial army at Rheinfelden. His capture of Breisach in December severed the Spanish Road, while Charles I Louis raised an army to regain his father's possessions in the Palatinate. Although the latter was routed by von Hatzfeldt at Vlotho in October, lack of supplies obliged Gallas to withdraw from the Baltic.

In April 1639, Banér defeated the Saxons at Chemnitz, then invaded Bohemia in May. To retrieve the situation, Ferdinand diverted Piccolomini's army from Thionville, ending direct military cooperation between Austria and Spain. Pressure grew on Olivares to make peace, especially after French and Swedish gains in Germany cut the Spanish Road, forcing Spain to resupply their armies in Flanders by sea. Attempts to re-assert maritime control ended when the Dutch fleet under Maarten Tromp won a significant victory over the Spanish at the Downs in October 1639.

The French occupied Spanish-controlled Artois in 1640, while Dutch attacks on Portuguese colonies, combined with opposition to taxes, led to revolts in both Portugal and Catalonia. Olivares now argued Spain should accept Dutch independence, and focus on preventing further French gains in the Spanish Netherlands. This appeared achievable since most of the Dutch regenten believed the war was won, the only question being the price of peace. They therefore reduced the army budget for 1640, despite objections from Frederick Henry.

After Bernard died in July 1639, his troops joined Banér's Swedish army in an ineffectual campaign along the Weser, the highlight being a surprise attack in January 1641 on the Imperial Diet in Regensburg. Forced to retreat, Banér reached Halberstadt in May where he died, and despite beating off an Imperial force at Wolfenbüttel in June, his largely German troops mutinied due to lack of pay. The situation was saved by the arrival of Lennart Torstensson in November with 7,000 Swedish recruits and enough cash to satisfy the mutineers.

The French won a victory at Kempen with Hessian support in January 1642. This was followed by a Swedish victory at Breitenfeld in October 1642, where Torstensson inflicted almost 10,000 casualties on an Imperial army led by Archduke Leopold Wilhelm of Austria. The Swedes captured Leipzig in December, although they failed to take Freiberg, and by 1643 the Saxon army had been reduced to a few isolated garrisons. Despite these setbacks, Ferdinand fought on, hoping to improve his position enough to exclude the Imperial Estates from his peace negotiations with France and Sweden, and allow him to represent the Empire as a whole.

This seemed more likely when Richelieu died in December 1642, followed by Louis XIII in May 1643, leaving his five-year-old son Louis XIV as king. However, Richelieu's policies were continued by his successor Cardinal Mazarin, while gains in Alsace allowed France to focus on the war against Spain. In 1643, the Army of Flanders invaded northern France, but were decisively beaten by Condé at Rocroi on 19 May. This ended any prospect of re-opening the Spanish Road, and Madrid finally accepted the reality of Dutch independence.

However, Condé was unable to fully exploit his victory due to factors affecting all combatants. The devastation inflicted by 25 years of warfare meant armies spent more time foraging than fighting, forcing them to become smaller and more mobile, with a much greater emphasis on cavalry. Difficulties in gathering provisions meant campaigns started later, and restricted them to areas that could be easily supplied, usually close to rivers. In addition, the French army in Germany was shattered at Tuttlingen in November by Bavarian general Franz von Mercy.

Soon after Rocroi, Ferdinand invited Sweden and France to attend peace talks in the Westphalian towns of Münster and Osnabrück, but negotiations were delayed when Christian of Denmark blockaded Hamburg and increased toll payments in the Baltic. This severely impacted the Dutch and Swedish economies, and in December 1643 the Torstensson War began when the Swedes invaded Jutland with Dutch naval support. The Swedish attack on Jutland, commanded by Torstensson, was accompanied by another invasion through Scania, led by Gustav Horn. Ferdinand assembled an army under Gallas to attack the Swedes from the rear and to support Denmark, which proved a disastrous decision. Leaving Wrangel to finish the war in Denmark, in May 1644 Torstensson marched back into Germany. Gallas was unable to stop him, and the Danes sued for peace after their defeat at Fehmarn in October 1644.

In August 1644, the French and Bavarian armies met in the three day Battle of Freiburg, in which both sides suffered heavy casualties. Convinced the war could no longer be won, Maximilian now put pressure on Ferdinand to end the conflict. Shortly after peace talks restarted in November, Gallas' army disintegrated and the remnants retreated into Bohemia, where they were scattered by Torstensson at Jankau in March 1645. In May, Bavarians under von Mercy destroyed a French detachment at Herbsthausen, before he in turn was defeated and killed at Second Nördlingen in August. In September, John George of Saxony signed a six-month truce with Sweden, then agreed to remain neutral in the March 1646 Treaty of Eulenberg.

Under Turenne, French commander in the Rhineland, and Wrangel, who had replaced Torstensson, the French and Swedes separately invaded Bavaria in the summer of 1646. Maximilian was soon desperate to end the war he was largely responsible for starting, at which point the Spanish publicised a secret offer by Mazarin to exchange French-occupied Catalonia for the Spanish Netherlands. Angered by this duplicity, the Dutch agreed a truce with Spain in January 1647 and began to negotiate their own peace terms. Having failed to acquire the Netherlands through diplomacy, Mazarin decided to do so by force. To free up resources for the attempt, on 14 March 1647 he signed the Truce of Ulm with Bavaria, Cologne and Sweden.

The planned offensive fell apart when Turenne's mostly German troops mutinied, while Bavarian general Johann von Werth refused to comply with the truce. Although the mutinies were quickly suppressed, Maximilian felt obliged to follow Werth's example, and in September ordered Bronckhorst-Gronsfeld to combine the remnants of the Bavarian army with Imperial troops under Peter von Holzappel. Outnumbered by a Franco-Swedish army led by Wrangel and Turenne, they were defeated at Zusmarshausen in May 1648. Holzappel was killed, and although most of his army escaped thanks to Raimondo Montecuccoli, Bavaria was left defenceless once again.

The Swedes sent a second force under von Königsmarck to attack Prague, seizing the castle and Malá Strana district in July. The main objective was to gain as much loot as possible before the war ended; they failed to take the Old Town but captured treasures including the Codex Gigas, which can now be seen in Stockholm. When a Spanish offensive in Flanders ended with defeat at Lens in August 1648, Ferdinand finally agreed terms and on 24 October, he signed peace treaties with France and Sweden, ending the war.

Control of Northern Italy provided access to the vulnerable southern borders of France and Austria. It also contained large sections of the Spanish Road, which allowed Spain to safely move recruits from Italy to support their war in the Netherlands. The French sought to disrupt this vital supply route by attacking the Spanish-held Duchy of Milan, or blocking the Alpine passes.

In 1618, war broke out in the Valtellina between the Catholic Grisons Rebels and the Protestant Three Leagues. Both Spain and France sent troops to support different factions, with France sending the Duke of Rohan and Spain the Duke of Feria. In 1625, Savoy invaded Genoa with French support, while François d'Estrées invaded the Valtellina. Spain then sent the Duke of Feria and the Marquess of Santa Cruz to relieve Genoa, which happened in April 1625. In 1626, France and Spain signed the Treaty of Monzón, with France agreeing to withdraw from the Valtellina and Piedmont.

Montferrat and its fortress of Casale Monferrato were subsidiary territories of the Duchy of Mantua and their possession allowed the holder to threaten Milan. When the Duke of Mantua died in December 1627, France and Spain backed rival claimants, resulting in the 1628 to 1631 War of the Mantuan Succession. The French-born Duke of Nevers was backed by France and the Republic of Venice, his rival the Duke of Guastalla by Spain, Ferdinand II, Savoy and 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.

In March 1629, the French stormed Savoyard positions in the Pas de Suse, lifted the Spanish siege of Casale, and captured Pinerolo. 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. 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.

Several factors restored the French position in northern Italy, notably a devastating outbreak of plague; between 1629 and 1631, over 60,000 died in Milan and 46,000 in Venice, with proportionate losses elsewhere. Richelieu took advantage of the diversion of imperial resources to fund a 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.

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 Tornavento and Mombaldone. 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 and Maurice.

In 1639, their quarrel erupted into open warfare, with France backing Christine and Spain the two brothers, and resulted in the 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.

In 1647, a French-backed rebellion succeeded in temporarily overthrowing Spanish rule in Naples. The Spanish quickly crushed the Neapolitan Revolt of 1647 and restored their rule over all of southern Italy, defeating multiple French expeditionary forces sent to back the rebels. 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.

Throughout the 1630s, tax increases levied to pay for the war led to protests throughout Spanish territories, which in 1640 resulted in revolts: first in Portugal with the Restoration War to re-gain their independence against the Iberian Union, then in the Principality of Catalonia. Both were backed by France as part of Richelieu's 'war by diversion', in January 1641 the rebels proclaimed a Catalan Republic. The Madrid government quickly assembled an army of 26,000 men to crush the Catalan revolt, which defeated the rebels at Martorell on 23 January 1641. The French now persuaded the Catalan Courts to recognise Louis XIII as Count of Barcelona, and ruler of Catalonia.

On 26 January, a combined French-Catalan force routed a larger Spanish army at Montjuïc and secured Barcelona. However, the rebels soon found the new French administration differed little from the old, turning the war into a three-sided contest between the Franco-Catalan elite, the rural peasantry, and the Spanish. There was little serious fighting after France took control of Perpignan and Roussillon, establishing the current-day Franco-Spanish border in the Pyrenees. The revolt ended in 1651 when Madrid recaptured Barcelona.