The Thirty Years' War: generals and great battles (1635-1643)

The declaration of war on Spain, on 19 May 1635, committed France to a conflict that had been open since 1618, with the Defenestration of Prague, and that had already gone through the successive phases of Bohemia, Denmark and then Sweden before France’s intervention. This direct entry into the Thirty Years’ War revived, in a new form, the anti-Habsburg “Grand Design” that Henry IV had been unable to carry through; it required of Richelieu a thorough reorganisation of the royal army and resulted, beyond the already familiar episode of the year of Corbie, in a series of sieges and battles that brought French military power to its height.

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🏛️ A transformed army

From the feudal army, made up of temporary, poorly professionalised and poorly funded levies, Richelieu forged a permanent instrument: professionalised regiments, a hierarchy clarified along lines of relative meritocracy, standardised artillery. Troop numbers followed a spectacular rise, growing from about 150,000 men in 1635 to nearly 200,000 in 1640, making the French army the largest in Europe — at the cost of a considerably heavier military budget and a fiscal pressure detailed elsewhere in other zooms of this chapter. This new army was notable for the integration of foreign commanders who had entered French service, such as the German Protestant prince Bernard of Saxe-Weimar, whose troops, known as the “Weimarians,” joined the royal army upon his death in 1639.

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🏰 Decisive sieges: Breisach, Arras, Perpignan

After the crisis of the year of Corbie was overcome in November 1636, the war continued through a series of sieges that gradually secured France control of strategic strongholds on its eastern, northern and southern margins. In December 1638, after a blockade lasting several months, Bernard of Saxe-Weimar captured Breisach, the fortress commanding the upper Rhine, giving France a lasting base for its operations in Germany. Two years later, on 9 August 1640, the royal army took Arras, capital of Spanish Artois, the first major city of the Spanish Netherlands conquered by France, after repelling a relief attempt of 25,000 men.

On the Pyrenean front, the revolt of Catalonia against Spain, in 1640, opened an unexpected opportunity for France: a treaty signed at Péronne on 19 September 1641 placed Roussillon and Cerdagne under the sovereignty of Louis XIII, while the siege of Perpignan, begun on 4 November 1641, ended on 9 September 1642 with the capitulation of the Spanish garrison, decimated by hunger — granting the French crown, only a few days before the execution of Cinq-Mars, the lasting annexation of Roussillon, which it was never to lose again.

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🎖️ Rocroi and the young generation of generals

It was, however, the battle of Rocroi, on 19 May 1643 — barely five days after the death of Louis XIII —, that was to crown this military effort. Facing the 27,000 Spaniards of Francisco de Melo, reputed invincible for decades, the young Duke of Enghien, the future Grand Condé, only twenty-one years old, personally led the cavalry charge which, outflanking the Spanish infantry from the rear, caused its complete rout: 8,000 dead and 7,000 prisoners on the Spanish side, against about 4,000 killed in the French ranks. This victory, won on the very morrow of the king’s death, put an end to the myth of the invincibility of the Spanish infantry and demonstrated the continuity of French military power beyond the change of reign. Alongside him the Viscount of Turenne was already distinguishing himself, the son of the Duke of Bouillon who had entered French service in 1630, whose methodical prudence contrasted with Condé’s boldness but whose career, begun under the orders of Bernard of Saxe-Weimar at Breisach, was to assert itself in the decades that followed.

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🧠 Key takeaways

• Reorganised by Richelieu, the royal army grew from about 150,000 men in 1635 to 200,000 in 1640, becoming the largest in Europe
• After the year of Corbie, France seized Breisach (1638), the lock on the upper Rhine, then Arras (1640) in the Spanish Netherlands, and annexed Roussillon following the siege of Perpignan, completed on 9 September 1642
• On 19 May 1643, five days after the death of Louis XIII, the victory of the young Duke of Enghien (the future Grand Condé) at Rocroi ended the myth of Spanish invincibility and revealed, alongside Turenne, the generation of generals that was to dominate the following decades