How Did Napoleon Actually Lose the Battle of Waterloo?

On the morning of 18 June 1815, Napoleon had reasonable grounds for confidence. He had beaten the Prussians under Blücher at Ligny two days before, and at Waterloo he fielded roughly 72,000 men against Wellington's roughly 68,000, with an edge in artillery. Napoleon's army faced the Duke of Wellington and his British-led coalition army, which was reinforced by Blücher's Prussian troops later in the battle, and at the start of the battle, the situation was not in the least unfavourable to Napoleon. He had beaten the Prussians at Ligny two days earlier and believed that he had neutralised their threat by sending an army corps under Marshal Grouchy after them. The plan rested on two assumptions that both proved wrong: that the Prussians were retreating away from the battlefield, and that Wellington's mixed Anglo-Dutch-German army would break under a direct assault before Blücher could intervene.

Heavy overnight rain had turned the clay soil of the Mont-Saint-Jean escarpment to mud, and this shaped the day before a shot was fired. Due to the conditions created by the heavy rains of the night before, Napoleon was forced to delay his attack on Wellington's forces, and the rain had a devastating effect on his army for a variety of reasons, leading to copious amounts of mud covering the battlefield, which made cannons difficult to maneuver, scattered French forces, and reduced cannons' effectiveness. The attack ultimately began at around 11 o'clock, far beyond Napoleon's initial plan to begin his assault at first light. Historians dispute how much the mud itself mattered versus simple deployment time: it has often been said that Napoleon delayed his attack to allow the ground to dry out, but in reality the additional time would have had little effect on the firmness of the ground, and the delay is more likely to have been to allow troops to move into position. Either way, the effect was the same: Wellington was happy to see Napoleon delay his attack, as every minute of delay meant that Prussian help would be more likely to arrive from Wavre in time to make a difference. A persistent theory attributes the delay partly to Napoleon's health -- one author and historian wrote a book arguing Napoleon suffered an acute attack of hemorrhoids that stopped him from riding his horse and keeping up his mobile supervision of troop movements -- but the leading modern biographical account disputes this as a sufficient explanation, since Napoleon was dressed and in saddle by 8 a.m. that morning.

The single decision most historians treat as decisive was Napoleon's dispatch of roughly a third of his army under Marshal Grouchy to pursue the defeated Prussians, on the assumption they were retreating toward the Rhine rather than regrouping to rejoin Wellington. Napoleon sent a third of his forces to pursue the Prussians, which resulted in the separate Battle of Wavre with the Prussian rear-guard on 18–19 June and prevented that French force from participating at Waterloo. The pursuit was itself sluggish: Napoleon wasted the morning of 17 June with a late breakfast and touring the previous day's battlefield before organising a pursuit of the two Coalition armies. Napoleon and Grouchy assumed that the Prussians were retreating towards Namur and Liège to take up a line on the river Meuse, but at the end of 17 June his detachment was behind the Prussians, on the far side of the Dyle; Grouchy could neither prevent the Prussians at Wavre from moving to Waterloo, nor regroup with Napoleon on 18 June at Waterloo. When the sound of the Waterloo cannonade reached Grouchy at midday, his subordinates urged him to march toward it; Grouchy's corps commanders, especially Gérard, suggested that they should march to the sound of the guns, but Grouchy had written and verbal orders from Napoleon to march on Wavre and to engage the Prussians there, and knew that Marshal Ney had been taken to task by Napoleon two days earlier for not following orders at Quatre Bras, so Grouchy declined to follow his subordinates' suggestion, pointing out that Napoleon already had sufficient numbers to defeat Wellington. The result, according to the specialist study of this phase of the campaign, is that Grouchy engaged a Prussian rearguard at the simultaneous Battle of Wavre, and although he won a tactical victory his failure to prevent the Prussians marching to Waterloo meant that his actions contributed to the French defeat.

On the field itself, Napoleon's attack unfolded in stages that each consumed strength without breaking Wellington's line. He opened with a diversionary assault on the fortified farm of Hougoumont, intended to draw off Wellington's reserves; instead it escalated into an unplanned battle of its own. He launched a feint attack on Wellington's right, aiming to threaten the chateau of Hougoumont and force Wellington to commit his reserves, but the plan backfired as Wellington steadfastly refused to commit more men, not least because they weren't needed, and the attack on Hougoumont escalated into a siege within a battle. The main infantry assault by d'Erlon's corps against Wellington's centre-left was then broken by a British cavalry counter-charge, though the British horse overextended and was in turn cut up by French cavalry -- a pattern of local, uncoordinated actions rather than a single decisive stroke. The most contested episode of the day came around 4 p.m., when Marshal Ney committed the massed French cavalry against the Allied line without infantry or artillery in close support. While Ney was engaged in the glorious but futile 8,000-man cavalry attack, unsupported by infantry or cannon, on Allied squares on the Brussels side of the ridge, he failed to take La Haye Sainte. At Waterloo the four-rank squares of the Allied forces withstood eleven cavalry charges. Why Ney attacked this way remains disputed among historians: it seems the Marshal was merely the victim of one of Wellington's clever ruses -- when the Iron Duke saw the French horse massing, he pulled his infantry back behind the slopes so they might form square unseen, and Ney took this to mean they were retreating and launched his troopers, thinking artillery and infantry support were unnecessary. Some accounts hold Napoleon, not Ney, ultimately responsible for the decision, since Napoleon makes it clear that he was in full command during the battle -- he, not Ney, had ordered the unsupported cavalry attack, not because he'd lost his mind, but because the infantry reserves had their hands full elsewhere.

The battle's outcome turned on a race Napoleon lost. While Ney's cavalry bled itself against the Allied squares, Blücher's Prussians -- reorganised after Ligny far faster than Napoleon and Grouchy had judged possible -- began arriving on the French right flank in the early evening. Wellington withstood repeated attacks by the French throughout the afternoon of 18 June and was eventually aided by the progressively arriving 50,000 Prussians who attacked the French flank and inflicted heavy casualties. With his right flank collapsing, Napoleon committed his last uncommitted reserve, the senior battalions of the Imperial Guard, against Wellington's centre. In the evening, Napoleon assaulted the Anglo-allied line with his last reserves, the senior infantry battalions of the Imperial Guard. The attack failed, and with the Prussians breaking through on the French right flank, the Anglo-allied army repulsed the Imperial Guard, and the French army was routed. Wellington's own verdict, recorded after the battle, was that it had been "the nearest-run thing you ever saw in your life" -- a judgment that later historiography has generally not overturned, even while it has debated exactly which of Napoleon's decisions made the difference.

Rich in tactical detail on individual episodes like the cavalry charges, but written after the fact and coloured by national pride or blame-shifting.

These fix the timing and content of key orders (such as the repeated instructions sent to Grouchy) but Napoleon's later memoir account is known to differ from his actual orders on record.

Modern reconstructions (drawing on regimental returns and terrain surveys) give reasonably convergent troop numbers and timings, though French casualty figures remain more disputed than British or Prussian ones.

Rests on late, secondhand testimony reported decades after the event and is treated by most military historians as a minor or unproven factor rather than an explanation for the defeat.

Would settle itA precise timed reconstruction of troop movements from unit war diaries and orders, comparing when units were actually in position against when the ground objectively became passable.

Would settle itSurviving timed orders passing between Napoleon's headquarters and Ney's command during the mid-afternoon of 18 June, which are incomplete or lost for this critical period.

Would settle itContemporary medical records from the campaign, which do not survive in sufficient detail; the claim rests on secondhand testimony from Napoleon's brother Jérôme, related decades later.

The beliefNapoleon lost at Waterloo mainly because he was simply outgeneraled by Wellington in a straightforward tactical duel.

The recordContemporary and modern accounts attribute the defeat to a combination of factors beyond direct tactical contest with Wellington: the delayed start, the diversion of Grouchy's wing, uncoordinated attacks by subordinates, and above all the arrival of Blücher's Prussian army on the French flank, which most military historians treat as decisive rather than any single tactical error by Wellington.

The beliefWellington's army at Waterloo was a purely British force.

The recordWellington's army was a multinational Anglo-allied force; the National Army Museum notes his roughly 68,000 troops were drawn from British, Dutch, Belgian, German and other allied contingents, not the British army alone.

The beliefThe rain the night before Waterloo is the single, agreed cause of Napoleon's late start and thus of his defeat.

The recordSpecialist campaign historians dispute how much the mud itself, as opposed to simple troop redeployment time, actually delayed the attack, and note the rain also slowed the Prussian advance to the battlefield, cutting both ways rather than favoring one side cleanly.

Wikipedia's Battle of Waterloo infobox, compiling modern strength estimates, gives the French army at 72,000–73,000 and Wellington's at approximately 68,000.

Wikipedia's Battle of Wavre infobox lists Grouchy's strength at 32,000–33,000 with 80 guns, engaged against Prussian forces of 17,000–24,000.

Multiple secondary military-history sources (HistoryNet, HistorySkills, the Napoleonic Archive) converge on an opening between roughly 11:00 and 11:30 a.m., though exact minute-level timing varies slightly between accounts.

Wikipedia's Battle of Waterloo entry and Blücher's army strength figures (approx. 50,000 soldiers) are consistent across the sourced order-of-battle data.

Britannica and Warfare History Network both give 25,000 killed/wounded and 9,000 captured, while Wikipedia's infobox gives a range of 26,000–27,000 casualties with 8,000 captured; other sources note French totals cited elsewhere range as high as 40,000, reflecting genuinely disputed figures.

Britannica gives Wellington's casualties as 15,000 and Blücher's as about 8,000; Wikipedia's infobox gives Wellington's army at 17,000 (3,500 killed, 10,200 wounded, 3,300 missing) and Blücher's at 6,604–7,000.

Wikipedia's La Haye Sainte article describes an '8,000-man cavalry attack, unsupported by infantry or cannon'; MilitaryHistoryNow describes '40 squadrons (more than 8,000 mounts)'.

Wikipedia's account of the Waterloo campaign (Ligny through Wavre to Waterloo) states Grouchy was at Sart-lez-Walhain when at about 11:30 he and his staff heard the cannonade, 23 kilometres from Waterloo.

Medical-history literature (Diseases of the Colon & Rectum, 1988) and biographer Andrew Roberts both acknowledge the affliction as documented via testimony from Napoleon's brother Jérôme, but Roberts and other historians dispute that it explains the delayed attack, since Napoleon was reportedly mounted by 8 a.m.

Field, Andrew W., Grouchy's Waterloo: The Battles of Ligny and Wavre (2017)scholarly

A detailed French-perspective study of Grouchy's pursuit and the Battle of Wavre, directly addressing the long-standing controversy over Grouchy's role in the defeat.

Cornwell, Bernard, Waterloo: The History of Four Days, Three Armies, and Three Battles (2014)accessible

A widely read narrative account by a novelist-historian that reconstructs the campaign hour by hour for general readers using published primary accounts.

Clausewitz, Carl von, The Campaign of 1815 in France (On Waterloo) (c. 1835)primary source

A near-contemporary professional military analysis by a leading strategic theorist, offering a detailed critique of Grouchy's and Napoleon's decisions written within two decades of the battle.

Napoleon commanded roughly 72,000 men against Wellington's approximately 68,000 at the start of the Battle of Waterloo on 18 June 1815.

Wikipedia's Battle of Waterloo infobox, compiling modern strength estimates, gives the French army at 72,000–73,000 and Wellington's at approximately 68,000.

Napoleon divided his army before Waterloo, sending Marshal Grouchy with about 32,000–33,000 men to pursue the Prussians, resulting in the separate Battle of Wavre on 18–19 June.

Wikipedia's Battle of Wavre infobox lists Grouchy's strength at 32,000–33,000 with 80 guns, engaged against Prussian forces of 17,000–24,000.

The Battle of Waterloo opened at around 11:30 a.m., several hours later than Napoleon's original plan.

Multiple secondary military-history sources (HistoryNet, HistorySkills, the Napoleonic Archive) converge on an opening between roughly 11:00 and 11:30 a.m., though exact minute-level timing varies slightly between accounts.

Roughly 50,000 Prussian troops progressively arrived on the French flank during the afternoon and evening of 18 June, tipping the battle.

Wikipedia's Battle of Waterloo entry and Blücher's army strength figures (approx. 50,000 soldiers) are consistent across the sourced order-of-battle data.

French casualties at Waterloo totaled approximately 25,000 killed and wounded plus around 8,000–9,000 captured.

Britannica and Warfare History Network both give 25,000 killed/wounded and 9,000 captured, while Wikipedia's infobox gives a range of 26,000–27,000 casualties with 8,000 captured; other sources note French totals cited elsewhere range as high as 40,000, reflecting genuinely disputed figures.

Allied (Wellington's) casualties were around 15,000–17,000 and Prussian casualties around 7,000–8,000.

Britannica gives Wellington's casualties as 15,000 and Blücher's as about 8,000; Wikipedia's infobox gives Wellington's army at 17,000 (3,500 killed, 10,200 wounded, 3,300 missing) and Blücher's at 6,604–7,000.

Marshal Ney led a massed French cavalry charge of roughly 8,000–9,000 horsemen against Allied infantry squares without infantry or artillery support.

Wikipedia's La Haye Sainte article describes an '8,000-man cavalry attack, unsupported by infantry or cannon'; MilitaryHistoryNow describes '40 squadrons (more than 8,000 mounts)'.

Grouchy's corps heard the cannonade of the Waterloo battle at around 11:30 a.m. but did not march to join Napoleon, instead continuing toward Wavre.

Wikipedia's account of the Waterloo campaign (Ligny through Wavre to Waterloo) states Grouchy was at Sart-lez-Walhain when at about 11:30 he and his staff heard the cannonade, 23 kilometres from Waterloo.

Napoleon suffered from thrombosed hemorrhoids during the Waterloo campaign, and this is sometimes cited as contributing to his delayed and impaired generalship on 18 June.

Medical-history literature (Diseases of the Colon & Rectum, 1988) and biographer Andrew Roberts both acknowledge the affliction as documented via testimony from Napoleon's brother Jérôme, but Roberts and other historians dispute that it explains the delayed attack, since Napoleon was reportedly mounted by 8 a.m.

Was the delayed start to the battle caused mainly by the need to let the mud dry, or by the time needed to redeploy troops who had bivouacked scattered across the area?

The traditional account, repeated in many popular histories, holds that Napoleon deliberately delayed the assault specifically to let the sodden ground firm up for artillery and cavalry. vs Specialist campaign historians argue the extra hours would have made little difference to ground firmness and that the real cause was simply the time required to move troops into position after a night in the rain.

Did Marshal Ney's decision to launch massed cavalry charges without infantry or artillery support reflect his own misjudgment, or was it consistent with orders and circumstances set by Napoleon?

One reading treats it as Ney's personal blunder, mistaking Wellington's tactical repositioning of infantry behind the ridge for a general retreat and launching an unsupported charge on his own initiative. vs Napoleon's own later account claims he was in full command and that the cavalry attack proceeded because available infantry reserves were tied up fighting off the Prussians elsewhere on the field, implying the decision (or at least its continuation) was his.

Did Napoleon's physical health, particularly reported thrombosed hemorrhoids, materially impair his generalship on the day of the battle?

A long-standing popular and some medical-literature theory holds that acute pain from hemorrhoids, treated with leeches and laudanum, left Napoleon lethargic and less attentive to the battlefield that morning. vs Napoleon biographer Andrew Roberts and other military historians argue the timeline does not support this as a decisive factor, since Napoleon was reported dressed and on horseback by 8 a.m., and treat the theory as an after-the-fact excuse rather than an operative cause.

Exactly what orders passed between Napoleon and Marshal Ney regarding the cavalry charges in the mid-afternoon of 18 June cannot be fully reconstructed.

Without a complete order record, historians cannot definitively assign responsibility for the unsupported cavalry attacks between Ney's independent judgment and Napoleon's own command decisions.

The precise French casualty total at Waterloo cannot be fixed within a narrow range.

French army records were disrupted by the collapse and retreat, leaving estimates of killed and wounded ranging from about 25,000 to over 40,000 depending on the source.