Hundred Days 1815: Was Waterloo Inevitable?

Iron Standard — Update 2 · 7 September 2026. This revision removes the deterministic assumption that Waterloo simply “had to happen”. It separates the political probability of renewed war from the contingent military decisions that produced the campaign of 15–18 June, and tests the familiar blame placed on d’Erlon and Grouchy against the limits of the surviving record.

Waterloo feels inevitable because we know where the story ends. Napoleon returns from Elba. Europe declares against him. He marches into Belgium. Wellington and Blücher close in. The Imperial Guard recoils and the Empire collapses.

But history did not move towards Mont St Jean on rails.

By March 1815 another major war involving Napoleon had become highly probable. The exact campaign that followed — the crossing at Charleroi, the twin battles of Ligny and Quatre Bras, the Prussian retreat to Wavre, Grouchy’s pursuit and Wellington’s stand south of Brussels — depended on decisions that could have gone differently.

The Iron Standard question is therefore not “why did Waterloo have to happen?” It is: which parts of the Hundred Days were structurally driven, and which were contingent?

The evidence: politics, orders and memoir wars

The Hundred Days is unusually well documented, but abundance creates its own problem. Commanders and staff officers wrote afterwards with reputations to defend. National histories turned a coalition campaign into competing British, Prussian and French stories. Later memoirs often sharpened uncertain conversations into memorable quotations.

• Political documents: the Allied declaration of 13 March and renewed alliance of 25 March show how rapidly the great powers treated Napoleon’s return as a common security problem.
• Operational orders and dispatches: these are essential for reconstructing intent, but an order proves what was written or reported — not necessarily what the recipient understood, when it arrived, or what the battlefield looked like on receipt.
• Post-battle dispatches: Wellington’s official account and French and Prussian reports are first-order evidence, but each was also written for governments, armies and public audiences.
• Memoirs and later histories: indispensable for detail, dangerous when several authors repeat a story derived from one earlier source.

This is why the campaign’s most famous questions — d’Erlon between two battlefields, Grouchy and the sound of the guns, Wellington’s dispositions, Napoleon’s timings — remain debated after two centuries.

1814: Napoleon was removed, not the European problem

Napoleon abdicated in April 1814 after coalition armies entered France. Louis XVIII returned, while Napoleon received sovereignty over Elba. The victors then met at the Congress of Vienna to reconstruct Europe after more than two decades of revolutionary and Napoleonic warfare.

The coalition powers had serious disagreements. Poland, Saxony, the balance between Russia and Prussia, the future of Germany and the territorial settlement all produced tension. Napoleon could therefore hope that the alliance that had beaten him might prove less coherent in peace.

That hope was not irrational. It was also rapidly overtaken by events.

March 1815: the political window closes

Napoleon left Elba on 26 February, landed near Cannes on 1 March and entered Paris on 20 March as royal resistance melted away.

Before he reached the capital, the powers at Vienna had already issued their declaration of 13 March 1815, describing him as an enemy and disturber of the peace. On 25 March Britain, Austria, Prussia and Russia renewed their alliance and committed themselves to major military effort.

That does not prove that diplomacy was literally impossible under every conceivable circumstance. It does show that Napoleon faced a coalition whose principal powers had rapidly subordinated their Vienna disputes to the problem of his return.

Iron Standard assessment: by late March, renewed large-scale war was very probable. A peaceful acceptance of Napoleon as restored emperor by the existing coalition system was highly unlikely.

Primary route: Declaration of the Allies, 13 March 1815.

Why Napoleon chose the offensive

Napoleon’s strategic problem was time. Coalition armies were mobilising on several fronts. If he remained passive, France would eventually face forces much larger than the army he could assemble quickly.

The most immediate opportunity lay in the Netherlands. Wellington’s Anglo-Allied army was dispersed to the west and Blücher’s Prussians to the east. Napoleon could concentrate faster than either opponent expected, move through Charleroi and try to occupy the central position between them.

The operational logic was classic: separate, concentrate, defeat in sequence.

Sometimes a further claim is made — that one spectacular victory would necessarily have split the coalition politically and forced peace. That is possible as a hope, but much harder to prove as a guaranteed consequence. The March agreements show a coalition already committed to Napoleon’s removal. A victory in Belgium could have improved his position; it did not automatically promise diplomatic collapse.

15 June: operational surprise, but not frictionless success

The French crossed the Sambre on 15 June and drove north through Charleroi. The move achieved genuine operational surprise and threatened the junction between Wellington and Blücher.

But the campaign was never the perfectly controlled machine sometimes imagined in hindsight. Roads clogged. Units arrived at different times. Staff work and verbal instructions generated uncertainty. Napoleon had gained the central position; he still had to convert it into the destruction of one coalition army before the other could intervene.

16 June: Napoleon nearly gets the campaign he wants

Ligny

Napoleon defeated Blücher’s Prussians at Ligny — the last battlefield victory of his career. The Prussians suffered heavily and Blücher himself was injured.

The critical fact is not simply that Napoleon won. It is that the Prussian army was not destroyed.

A beaten army can remain strategically dangerous if its command structure, routes and political will survive. The Prussians withdrew towards Wavre rather than retreating eastward away from Wellington. That decision preserved the coalition relationship Napoleon had been trying to break.

Quatre Bras

At Quatre Bras, Marshal Michel Ney failed to seize the crossroads before Wellington’s force grew strong enough to hold it. The fighting was costly and confused. Wellington retained the position for the day but could not remain once he learned that the Prussians had been defeated at Ligny.

d’Erlon: the perfect scapegoat for an imperfect command system

I Corps under Jean-Baptiste d’Erlon is famous for spending part of 16 June moving between Ligny and Quatre Bras without delivering its full weight decisively at either.

It is tempting to write this as one absurd mistake: a corps of roughly 20,000 men wandering uselessly while two battles were fought nearby. The underlying problem was more serious and more interesting. Napoleon and Ney were directing related operations on separate battlefields, and orders changed while the corps was already moving.

Had d’Erlon arrived against the Prussian flank at the right moment, Ligny might have become more destructive. Had it remained fully available to Ney, Quatre Bras might have developed differently. Neither counterfactual is certain.

Iron Standard assessment: d’Erlon’s ineffective employment was a major lost opportunity. The claim that one single individual error “lost the campaign” on 16 June is unproved.

17 June: the Prussians make the decisive strategic choice

After Ligny, Napoleon expected the Prussians to be sufficiently damaged that they could be pursued and kept away from Wellington. He detached Marshal Emmanuel de Grouchy with a large force.

Blücher’s army instead concentrated around Wavre. Fondation Napoléon’s campaign chronology emphasises the importance of this withdrawal: by moving north and east rather than abandoning contact, the Prussians remained capable of supporting Wellington.

Wellington withdrew from Quatre Bras to Mont St Jean in heavy rain. By the evening, the coalition had survived the moment of greatest danger. One army had been defeated and the other forced back, but Napoleon had not separated them strategically.

Was Wellington’s stand dependent on Blücher?

Yes.

Wellington’s choice to fight at Mont St Jean is often presented as the solitary decision of a defensive genius selecting the perfect ridge. The ridge mattered. So did the promise of Prussian support.

Blücher and his staff agreed to march. That transformed Wellington’s position from an indefinite isolated defence into one half of a coalition operation. The question for 18 June was whether Wellington could remain intact until enough Prussians arrived.

Iron Standard assessment: Prussian support was not a late bonus added to a battle Wellington had already designed to win alone. It was fundamental to the coalition plan.

Grouchy and the sound of the guns

No figure in the campaign has been more conveniently blamed than Grouchy.

The popular story says that on 18 June he heard the guns of Waterloo, ignored advice to “march to the sound”, obeyed his orders too literally and thereby allowed Blücher to destroy Napoleon.

There is a real command problem underneath the legend. Grouchy failed to prevent major Prussian formations from reaching Waterloo. That mattered enormously. But the later controversy is not solved merely by repeating the anecdote.

Grouchy had orders to follow and observe the Prussians. Their movements were imperfectly known. His force was not standing on a clear road that led directly into Napoleon’s flank at the exact moment needed. He fought at Wavre and actually won there after the main battle had already been lost.

Fondation Napoléon’s own survey notes that Grouchy’s failure to reach Waterloo became one of the standard explanations for Napoleon’s defeat, while modern scholarship continues to dispute how much responsibility properly belongs to him. Specialist studies have even questioned whether some orders and later recollections used in the accusation were exactly what post-war writers claimed.

Iron Standard assessment: Grouchy failed in the operational purpose of keeping the Prussians away from Napoleon. Whether he could realistically have marched to Waterloo soon enough, in sufficient strength, under the orders and information he actually possessed, remains contested. Making him the sole cause of defeat is bad history.

18 June: Waterloo was now possible, not predetermined

By the morning of 18 June, Napoleon had Wellington in front of him and the Prussians regrouping to the east. The battle that followed still depended on battlefield events — Hougoumont, d’Erlon’s attack, the heavy cavalry counterattack, French cavalry assaults, the fall of La Haye Sainte, fighting around Plancenoit and the final commitment of the Imperial Guard.

Nothing in the political declaration of March guaranteed those events.

What the campaign had done was create a shrinking French margin for error. Napoleon had failed to destroy the Prussians at Ligny, failed to prevent their recovery, and entered the final battle while the two coalition armies were still capable of acting together.

So: was Waterloo inevitable?

Claim	Assessment
The coalition was likely to wage war to remove Napoleon after March 1815	Very probable
A major campaign somewhere was likely unless diplomacy changed radically	Very probable
The decisive battle had to occur at Mont St Jean on 18 June	False
Napoleon’s offensive into Belgium had coherent strategic logic	Strongly supported
d’Erlon’s movements were a serious lost opportunity	Very probable
The Prussian withdrawal to Wavre preserved the coalition plan	Central and strongly supported
Grouchy alone lost Waterloo by refusing to march to the guns	Over-simplified and contested
Wellington planned to defeat Napoleon indefinitely without Prussian support	Misleading

What would change our mind?

The key unresolved areas are command transmission and timing. Newly identified originals of disputed French orders, securely dated staff journals showing when they were sent and received, or independent accounts locating Grouchy’s formations more precisely at critical moments could materially alter assessments of responsibility.

Similarly, stronger evidence for Napoleon’s expected political consequences after a Belgian victory could refine the distinction between his military plan and the diplomatic hopes later attributed to it.

Why the campaign matters more than the myth

The Hundred Days was not a countdown to a pre-written defeat. Napoleon created a genuine operational crisis for the coalition on 15–16 June. He defeated the Prussians at Ligny and forced Wellington to retreat.

He failed at the harder task: turning those successes into separation and destruction.

The Prussian army’s recovery, the decision to remain in contact with Wellington and the coalition’s willingness to coordinate after defeat are therefore as important as any French mistake. Waterloo became possible because the coalition survived Napoleon’s best opportunity to prevent it from fighting as a coalition.

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SCHOLARLY CHALLENGE

Iron Regiment invites historians of the 1815 campaign to challenge the treatment of d’Erlon, Grouchy, Prussian intentions, the timing of orders and the political assumptions attributed to Napoleon. Where surviving documents support competing reconstructions, the disagreement should be shown rather than flattened into one national narrative.

Primary routes and further reading

• Declaration of the Allies, 13 March 1815 — Hansard archive — primary political evidence for the coalition response.
• National Army Museum — Hundred Days Campaign — operational overview.
• National Army Museum — Battle of Waterloo — battle and campaign context.
• Fondation Napoléon — Blücher and the Waterloo Campaign — useful Prussian-centred chronology of the recovery from Ligny and march from Wavre.
• Fondation Napoléon bibliography — Napoleon and Grouchy — route into the modern dispute over orders, evidence and scapegoating.

Continue to the battlefield

The campaign culminates at Mont St Jean. Continue with Waterloo 1815: How the Battle Unfolded.

For the tactical problem at the centre of the French cavalry attacks, read How Infantry Squares Stopped Cavalry.

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From the collection

Explore the Waterloo 1815 collection and the wider Revolution & Empire archive.

Revision record

Update 2 — 7 September 2026: Reframed the article from deterministic campaign narrative to an Iron Standard investigation. Added source genealogy, explicit treatment of d’Erlon and Grouchy as contested command problems, confidence grading, a coalition-centred interpretation, scholarly challenge and a “what would change our mind” section. Existing URL preserved.

Iron Standard Investigation. We do not repeat the historical record; we interrogate it. Where the evidence is uncertain, we say so.