The Battle of Malplaquet took place on 11 September 1709 during the War of the Spanish Succession and was fought between a French army commanded by the Duke of Villars and a Grand Alliance force under John Churchill, the Duke of Marlborough. In one of the bloodiest battles of the 18th century, the Allies won a narrow victory but suffered heavy casualties, while the French were able to withdraw in good order.

At the start of 1709, the French state seemed on the verge of collapse, its treasury empty and food scarce while Allied advances in 1708 left the kingdom open to an invasion. These factors made the Allies overconfident and their excessive demands led to the collapse of peace talks in April. Villars had been instructed to avoid battle but after the capture of Tournai in early September, the Allies moved against Mons and Louis XIV of France ordered him to prevent its loss. Although the two armies made contact on 10 September, Marlborough delayed his attack until the next day, giving Villars the opportunity to strengthen his defensive positions.

When the battle began on 11 September, Marlborough used his standard tactic of simultaneous infantry attacks on the flanks, forcing Villars to move troops from the centre, which would then be broken by a mass cavalry charge. While successful in other battles, at Malplaquet the French were better led, held stronger positions and were highly motivated; as a result, the flank attacks incurred heavy casualties, particularly on the left where the Dutch lost over 5,000 men in less than thirty minutes and nearly 8,500 in all. Although the overall plan worked, the French cavalry ensured their centre did not collapse as on previous occasions, while the Allied infantry was too weakened by their losses to conduct a pursuit, allowing the French to withdraw intact.

The Allies lost over 20,000 men in the battle, the French no less than 8,000, casualties which shocked contemporaries and heightened internal divisions within the Grand Alliance over the wisdom of continuing the war. It has been argued Malplaquet was a French strategic victory, since by saving his army and preventing an invasion of France, Villars ultimately enabled Louis to negotiate far better peace terms in 1713 than those available in 1709. While there is some truth to this, it did little to change the immediate strategic situation; Mons surrendered shortly afterward and the Allies resumed their advance in 1710. Some historians suggest the biggest impact of the battle was in restoring French military confidence after years of defeat.