Why did Napoleon lose the Battle of Waterloo?

Napoleon’s defeat at the Battle of Waterloo on June 18, 1815, resulted from a combination of strategic errors, poor coordination, and the arrival of Prussian reinforcements.1

Key factors contributing to the French loss included:

• Delayed Offensive: Napoleon delayed the start of his attack until midday to allow the ground to dry, which inadvertently provided the Prussian army under Gebhard Leberecht von Blücher the necessary time to reach the battlefield and support the Duke of Wellington.1
• Lack of Coordination: French attacks against Wellington’s center lacked coordination between infantry and cavalry, rendering them ineffective against British defensive squares.12
• Failure to Neutralize Enemies: Napoleon’s marshals, Ney and Emmanuel de Grouchy, failed to prevent the Prussian and Allied armies from uniting. Grouchy’s forces were tied down at Wavre, allowing Blücher’s main force to rejoin Wellington.1
• Preoccupation with Flanks: Napoleon was distracted by the Prussian pressure on his eastern flank, leading him to withhold critical Imperial Guard reinforcements from Ney at the decisive moment when the Allied center was vulnerable.13

By the time Napoleon committed his reserves, Wellington had reorganized his defenses, and the arrival of further Prussian reinforcements ensured the French collapse.13