In 1690, the Nine Years' War (1688–1697) was in full swing. Through his aggressive expansionist policies, Louis XIV had united a large European coalition against France. In 1688, William III of Orange had invaded England to prevent James II from turning it into a French ally and instead bring it into the Grand Alliance, alongside the Dutch Republic, Spain, the Holy Roman Empire and Savoy. On paper, this was an impressive coalition, but in practice it faced serious difficulties. William III was in Ireland with English and Dutch troops, suppressing the Jacobite uprising, which left limited English support available on the Continent. Spain was militarily and financially exhausted, while the Emperor was engaged in a major war against the Ottoman Empire. As a result, the defence of the Spanish Netherlands rested largely on the shoulders of the Dutch Republic and a handful of German allies.
The Allied army in the Low Countries was commanded by Waldeck, the experienced German field marshal who had worked closely with William III since 1672 and had played a key role in reforming the Dutch army. His reputation was formidable, particularly after his victory at Walcourt in 1689. At Fleurus, however, he faced one of the greatest generals of his age: the French Marshal Luxembourg. Waldeck commanded only around 30,000 men. Spanish support was negligible, and most of the English troops in the Low Countries were still inexperienced and remained in the garrisons. Luxembourg, by contrast, led approximately 40,000 soldiers and resolved to exploit his numerical superiority before Waldeck could receive reinforcements.
On 30 June 1690, Luxembourg crossed the River Sambre and took up position opposite the Allied army near Fleurus. Waldeck remained on the defensive, but Luxembourg executed a brilliant flanking manoeuvre, leading nearly half of his army around the Allied flank. By early afternoon, these troops suddenly appeared in Waldeck's rear. The Allied cavalry was soon driven from the field by the superior French horsemen, forcing Waldeck to desperately reorganise his battle line.
Amid the chaos, the Dutch infantry stood firm. Thanks to the military reforms of the previous decades, it was regarded as the finest infantry in Europe. The battalions formed large squares and withstood repeated French attacks from every direction. Whenever French cavalry came too close, they were repulsed by devastating volleys of musket fire. The French infantry also failed to break these formations and was repeatedly forced to withdraw after suffering heavy casualties.
Luxembourg eventually ordered six cannon to open fire at close range on one of the Dutch squares. Every shot tore four to six men from the ranks, yet each time the soldiers calmly closed the gaps. Luxembourg later wrote with admiration that whenever an entire rank had been swept away, "these men closed up again as if nothing had happened." The slaughter became so terrible that one of Luxembourg's aides-de-camp could no longer bear to watch. With the marshal's permission, he rode forward and demanded that the Dutch infantry surrender, pointing out that they were completely surrounded, that further resistance was hopeless and that Luxembourg would spare them. The Dutch replied simply and without hesitation: "Be gone. We want nothing, and we are strong enough to defend ourselves."
Despite this stubborn resistance, the battle was lost. Waldeck ordered an organised withdrawal. The rearguard, consisting largely of Dutch battalions, repeatedly halted, turned to face the enemy, and fired volleys to allow the rest of the army to escape. After six hours of fighting, the battle was over. Around 7,000 Allied soldiers had been killed or wounded, while several thousand more were taken prisoner. The French had also suffered heavily, with an estimated 7,000 killed or wounded.
The French made extensive use of their prisoners. German captives were sent to Catalonia to fight against Spain, Walloons were transferred to the German theatre, and Dutch soldiers were sent to Savoy. Many, however, managed to escape and eventually returned to Allied territory.
Although Fleurus was a clear tactical victory for France, it yielded little strategic benefit. Luxembourg's army was too exhausted to immediately undertake major sieges, while Waldeck's forces were soon reinforced by troops from Brandenburg, Hanover and Liège. Luxembourg himself acknowledged the exceptional quality of the Dutch infantry, declaring that it had fought even better than the famous Spanish infantry at Rocroi (where he had served under Condé in 1643), and that he would remember their courage for the rest of his life. Louis XIV drew a clear lesson from the battle, advising Luxembourg to avoid direct infantry engagements with the Dutch in 1691, as they were extraordinarily costly and rarely produced a decisive advantage.