France supported revolts against Spanish rule in Portugal (1640–1668), Catalonia (1640–1653) and Naples (1647), while Spain backed French rebels in the 1647 to 1653 civil war or "Fronde".

While relatively minor in extent, French territorial gains significantly strengthened their borders, while Louis XIV married Maria Theresa of Spain, eldest daughter of Philip IV.

In 1938, British historian Veronica Wedgwood argued that it actually formed part of a wider ongoing European struggle, with the Habsburg-Bourbon conflict at its centre.

[10] During the 1620s, France was threatened internally by a series of Huguenot rebellions and externally by Habsburg possessions on its borders in the Spanish Netherlands, Lorraine, Alsace, Franche-Comté and Roussillon.

Prior to 1635, France sought to weaken both branches of the Habsburgs by financing their opponents, including the Dutch, clients in Northern Italy and the Grisons, the Ottomans, the Venetian Republic, Transylvania and Sweden.

[17] The Thirty Years' War began in 1618 when the Protestant-dominated Bohemian Estates offered the Crown of Bohemia to Frederick V of the Palatinate, in place of the conservative Catholic Emperor Ferdinand II.

[21] A significant Imperial-Spanish victory at Nördlingen in September 1634 forced the Swedes to abandon southern Germany, and most of their German allies used the opportunity to make peace with Ferdinand II at Prague in April 1635.

The Spanish Empire reached its maximum nominal extent under Philip's rule, but its size and complexity made it increasingly difficult to govern, or enact essential reforms.

[24] However, its depth of resources consistently allowed it to recover from defeats that would have shattered other powers, and new regulations passed in 1631 and 1632 were key to the improved Spanish military performance in the first part of the war.

[28] Led by Cardinal-Infante Ferdinand of Austria, the Spanish took the initiative and captured Limbourg, Gennep, Diest and Goch and besieged Dutch garrisons in the Duchy of Cleves.

[32] With Spanish resources stretched to the limit in Europe, the Dutch used the opportunity to attack their possessions in the Americas, Africa and Asia, especially those belonging to the Portuguese Empire, which was also ruled by Philip IV.

[33] Damage to the economy and tax increases imposed to pay for the war led to protests throughout Spanish territories, which in 1640 erupted into open revolts in Portugal and Catalonia.

[37] It also gave Condé, a member of the royal family and the effective ruler of large parts of eastern France, leverage in his struggle with Anne and Cardinal Mazarin.

Under the October 1648 Treaty of Münster, France gained strategic locations in Alsace and Lorraine, as well as Pinerolo, which controlled access to Alpine passes in Northern Italy.

In addition, many of his best troops had been lost at Rocroi and parts of Flanders overrun, including the key port of Dunkirk, a centre for Spanish privateer attacks on Dutch and French shipping.

[42] Philip initially hoped simply to improve the terms on offer from France, but the Fronde allowed him to make substantial gains in the Netherlands, including retaking Ypres.

Under pressure from Pope Alexander VII, Mazarin offered peace terms but refused to accept Philip's insistence for Condé to be restored to his French titles and lands.

On 15 August, Spain won an important victory at Camprodon in Catalonia, Oliver Cromwell's death in September led to political chaos in England, and fighting in northern Italy ended when French allies Savoy and Modena agreed to a truce with the Spanish commander, Caracena.

Acquisition of Roussillon established the Franco-Spanish border along the Pyrenees, but divided the historic Principality of Catalonia, an event still commemorated each year by French Catalan-speakers in Perpignan.

[53] An integral part of the peace negotiations was the marriage contract between Louis and Maria Theresa, which he used to justify the 1666 to 1667 War of Devolution, and formed the basis of French claims over the next 50 years.

Although (its) economic and military power suffered an abrupt decline in the half century after (1659), (it) was a major participant in the European coalitions against Louis XIV, and the peace congresses at Nijmegen in 1678, and Ryswick in 1697".

[8] David Parrott, Professor of Early Modern History at New College, Oxford claims the Peaces of Westphalia and the Pyrenees both reflected mutual exhaustion and stalemate, not a "military diktat imposed by victorious powers".

[59] Taking on the Spanish Empire, then the strongest military power in Europe, required French forces of unprecedented size and an associated expansion of the taxation and supply base needed to support them.

[60] However, at this stage the French state was unable to support such large numbers; of the 27,000 men who took part in the invasion of the Spanish Netherlands in May of the same year, fewer than 15,000 remained a month later.

[61] These are based on official muster rolls and should be treated with caution, since officers were paid for numbers reported, rather than those actually present; in addition, during this period on average another 10% was absent due to sickness, although most generally recovered.

It was not until the 1660s that Louvois created the support systems that allowed France to sustain an army of nearly 200,000 men for extended periods, and crucially ensure co-ordinated strategy between different fronts.

These advantages could be offset by engaging them on multiple fronts while attacking their lines of communication, a tactic the French used throughout the war by supporting the Catalan, Neapolitan and Portuguese rebels along with allies in Northern Italy and the Rhineland.

The Grand Duchy of Tuscany, a de facto Spanish protectorate was required to supply 17,000 scudi a month, as well as provide ships for the fleet and soldiers for the Army of Flanders.

When the commander of the Army of Extremadura requested 3,000 quintales (138 tons) of gunpowder for the 1659 campaign in Portugal, the central Junta of War for Spain revealed that total supplies for defense in the peninsula (including the navy, coastal garrisons, and militia in addition to the three major war fronts in Catalonia, Extremadura and Galicia) were only 1427 quintales (66 tons) due to so much powder having been spent in the fight against France.

[70] In October 1647, discontent led to revolts in both Sicily and Naples; although quickly suppressed, it exposed the weakness of Spanish rule in Italy and the alienation of the local elites from Madrid.