Why did Marshal Ney’s cavalry attacks fail at the Battle of Waterloo?

Marshal Ney’s cavalry attacks at the Battle of Waterloo failed primarily because they were launched without the support of infantry or sufficient artillery.1

Ney initiated these charges after mistakenly interpreting the movement of wounded men and empty ammunition wagons from the British center as a sign that the front was weakening. When the French cavalry advanced, the British forces responded by forming infantry squares—hollow, multi-ranked defensive formations specifically designed to repel horsemen.1

Because the French cavalry lacked the necessary infantry to break these formations or the close artillery support to soften them, they were unable to overcome the unbroken British lines. Despite the determination of the 9,000 French cavalrymen involved, they suffered heavy losses from English gunners and were repeatedly driven back by the remaining British cavalry.1