Short answer:

Not the way leaders thought at the time. Don't think of Napoleon "like Hitler". Monarchs didn't want to see other monarchs executed.

Discussion:

Europe was trying to get away from the idea of the execution of monarchs-- the execution of Louis XVI was a particular horror. The other crowned heads of Europe were very much attached to the idea of . . . keeping them attached to their necks. Execution of monarchs wasn't a precedent they wanted to encourage, and Napoleon had been [mostly, with exceptions] recognized as a legitimate monarch, and had [again, mostly] not executed his defeated enemies. After his fall, Talleyrand would characterize the period of Revolution and Napoleonic rule as a usurpation of the legitimate, but that was casuistry -- Napoleon as an Emperor was regarded as such, and indeed often admired by other monarchs, notably Alexander of Russia.

Its notable that Leo Tolstoy opens War and Peace with a discussion of what at least some Europeans thought was perhaps the worst thing Napoleon did -- the kidnapping and execution of the Duc d'Enghien, the last descendant of the Grand Condé and a Bourbon. This could be held to be Napoleon's most "revolutionary" act, an occasion where he comes closest to the regicidal impulses of the Terror. He later disavows it -- suggests that its Talleyrand's doing (improbable). But it's the exception that proves the rule . . . though a usurper, he mostly "played by the rules" as they were understood at the time.

The monarchs thought of themselves as a family -- a usual term of address for a monarch writing another monarch was: "mon cousin"; Napoleon was married to Marie Louise of Austria. By this marriage, he even has a (not blood) tie to Louis XVI and Marie Antoinette. Family may be bad, mad, dangerous or belligerent. If sufficiently inconvenient they may need to be shut away someplace they can't do any harm, but royals didn't love the idea of another royal execution. One caveat to this is to note that the British had never recognized Napoleon as a legitimate Emperor-- he was, in British eyes, "General Bonaparte", but in that they differed from the Russians and Austrians.

Napoleon wasn't openly held to be a war criminal, nor was he uniformly unpopular, even in defeat. Waging aggressive war was not a breach of international law in the 18th and 19th century; in the 20th century its regarded as illegitimate, and you'll see at Nuremberg that among the charges laid against the Nazi defendants was "planning aggressive war". Its an anachronism to apply that reasoning to 1815; at that time, going to war was considered a natural, legal and even admired activity for nations. In an age still adhering to a feudal military tradition for political legitimacy, war was part of the system, not a breach. With that said, in the Secret Treaty of Vienna of January 1815, the Allies declare that Napoleon S'est mis hors de protection de la loi - has placed himself outside the protection of the law.

For a Briton, Napoleon had given them their greatest triumphs and their greatest heroes-- Nelson and Wellington and he and his cause had more than a little glamor. Charles de Flahaut, probably the son of Talleyrand and Napoleon's aide de camp at Waterloo finds his way to Britain fleeing the Bourbons. Two years later he marries the daughter of George Elphinstone, Admiral Lord Keith-- so the great admiral's son in law is one of Napoleon's generals. In fact, a fair number of DeBrett's Peerage are descended from the five daughters of this union. . . this gives a sense of the degree to which war and "the enemy" were understood quite differently in 1815. The contest of arms still had a glamor, and Napoleon, though an enemy, was part of Europe's heroic story.

So to analogize Napoleon to defeated Nazis or Japanese is anachronistic. While there was some sentiment to hang him, that was not the mood of the leaders of Europe. Hanging Emperors didn't seem like a great idea to other Emperors, and the precedent holds for a century. The Kaiser's treatment after World War I is similarly motivated to Napoleon's, the Allies did make an attempt to arraign him, but the Netherlands refused to hand him over, and so he ended up in his own effective exile.

The First and Second Abdications

Napoleon's removals from office were, technically and practically, abdications. This was an important political aim for the Allies. In 1814, he abdicates on his own behalf, and disclaims claims that might be made on behalf of his family . . . this is important to European monarchs, used to the idea of centuries of wars over hereditary claims.

This is an important distinction -- might just seem like words, but it mattered to the people at the time. Napoleon had something valuable to offer the Allies, even in defeat: his acquiescence. For men like Talleyrand, Metternich and Castlereagh, trying to rebuild a conservative order based around monarchy, the best way to dispose of a dangerous monarch was voluntarily, without execution or martyrdom.

The Restoration of the Bourbons was seen as a necessary but a very delicate project-- all were well aware that Napoleon was substantially more popular with the French than the exiled Louis XVIII and his family. Europe in 1814-15 was more afraid of the French Revolution than they were of Napoleon, and this fear wasn't misplaced-- the prospect of "Peterloo" (the 1819 attack on a crowd of Lancashire protesters) more of a threat to the regimes than Waterloo.

Sources:

Robertson, Charles Grant. “GREAT BRITAIN AND NAPOLÉON, 1814–15.” History, vol. 29, no. 109, 1944, pp. 27–43.

Kissinger, Henry. "A World Restored"

Rie, Robert. “The Origins of Public Law and the Congress of Vienna.” Transactions of the Grotius Society, vol. 36, 1950, pp. 209–227.

NOËL, LÉON. “AU CONGRÈS DE VIENNE: LES SOUCIS DE M. DE TALLEYRAND.” Revue Des Deux Mondes (1829-1971), 1965, pp. 13–27.

Jarrett, Mark. “No Sleepwalkers: the Men of 1814/15. Bicentennial Reflections on the Congress of Vienna and Its Legacy.” Journal of Modern European History / Zeitschrift Für Moderne Europäische Geschichte / Revue D'histoire Européenne Contemporaine, vol. 13, no. 4, 2015, pp. 429–438.

Hathaway, Oona and Shapiro, Scott. "The Internationalists: How a Radical Plan to Outlaw War Remade the World" (Simon & Schuster:2017)

Hey there,

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