Why did Napoleon’s Imperial Guard fail in its final attack at Waterloo?

The failure of Napoleon’s Imperial Guard during their final attack at the Battle of Waterloo on June 18, 1815, was primarily due to the timing and the resilience of the Allied defenses.1

By the time Napoleon finally released the Imperial Guard to Marshal Michel Ney after 7:00 pm, the opportunity for a decisive breakthrough had passed. Earlier in the day, Napoleon had been preoccupied with a flanking attack by Prussian forces, which forced him to delay sending reinforcements to the center of the battlefield.1

During this delay, the duke of Wellington had successfully reorganized his defensive lines, bolstered by the arrival of a Prussian corps under Hans Ernst Karl von Zieten. When the Guard eventually launched their assault, they were met with concentrated firepower from the Allied infantry, which shattered the tightly packed formations of the French veterans. The repulse of the Guard at 8:00 pm signaled the collapse of the French position, leading to a disorganized retreat and the final defeat of Napoleon.1