Another Philip succeeded as head of the Spanish Empire in 1621. In his time the castle's restoration was completed in 1625 and the town in 1631 gave 50,000 florins to borrow to pay off its debts. In 1635, France under the influence of Richelieu allied to the United Provinces (Dutch Protestant) and sent its heralds to the Grand Sablon Square in Brussels for a declaration of war against Spain dragging the southern Spanish Netherlands (including Hainaut) into the turmoil of the fourth phase so-called " French phase" of the Thirty Years War, between the French and Dutch versus a Hispano-Austrian-German alliance. Hainaut at that time was criss-crossed by all troops and vehicles of war and requisitions impoverished rural areas. This misfortune led to another ... in 1639, an epidemic became widespread throughout the region and many people perished in Le Quesnoy. In 1648, the Prince of Ligne came to Le Quesnoy with 4,000 men equipped with artillery and prepared to defense operations, which were needed to counter the advance of French troops. The following year, the property belonging to the French in the town was confiscated. On 31 August 1651 the Hispanic-Hainaut garrison at Le Quesnoy won one last success in the walls of the town. But on 4 September 1654 the Vicomte de Turenne, at the head of the French army, stood before Le Quesnoy with a powerful artillery: he seized the town whilst the Spanish before leaving tried to render useless the fortifications by damaging the most out of walls. Turenne became master, cleverly foiled the plans of Condé (the Great Condé, Duc d'Enghien, then in the service of Spain).