So watching this series has got me on a Napoleonic history kick.
What if after Leipzig, Napoleon managed to rally the French people for a people's war against the sixth coalition? As opposed to the populace being passive to indifferent, if not outright opposing him.
As in peasants and farmers attack allied armies, and kill allied soldiers whenever possible, every French city has to be taken in vicious street to street and house to house fighting.
First off, this goes beyond realism as the French people were exhausted and just wanted the wars to stop. But screw that, we want a guerre populaire totale. I don't know-maybe have it be known the allies intend to partition France and break their country into either small domains or outright annex chunks of the country for themselves. So a war for the sake of the nation.
What I imagine is this makes the campaign last longer-perhaps later into 1814, as every able bodied French man joins the cause, in either the army or in guerilla action.
Napoleon's genius with the people behind him allows him to smash the coalition, in battle, and hold the line...longer. Maybe have the French hold Paris longer-and fight to see the city a smoldering ruin.
Eventually though, by the middle of 1815-Napoleon is defeated, and exiled to the Azores, with France dismembered-The British gain Normandy, Brittany, and Aquitaine, The Prussians gain everything from Alsace to Calais, the Austrians gain Alpine France up to Burgundy, while Bourbon Spain acquires Languedoc, and Gascogne, with a rump Bourbon France holding the rest.
France's dismemberment leads to great suffering amongst the population, as the allied powers squabble over the spoils-leading to an outbreak between an Austro-Russian alliance and an Anglo-Spanish-Prussian alliance which shatters France even further, and exhausts the allies.
Leading to the destruction of the European state system-with Britain exhausted, and the monarchy overthrown, the French bourbons lynched, and the war between Prussia and Austria leading to their mutual ruin.
By 1830-Europe is devastated, with the old order and new ideals alike devolving into warlordism, ad hoc city states, and roving bandits made up of former soldiers.
Russia and the Ottomans are the last powers standing-with the Ottoman Sultan reforming the army and seeing the chaos in Europe-decides to revive the Turkish dream for a decisive push into Central Europe-the victory of the Crescent being at hand, only to met by Russian Empire which extends all the way to Berlin(in theory if not in practice). Leading to the struggle for the east, which ends with the Russians taking Constantinople and the Czar declared Roman Emperor, and Emperor of the Greeks, only to be assassinated in a palace coup a month later(this takes place in 1840).
Leading to Russia collapsing into another time of troubles, while an alt Muhummad Ali figure uses Egypt as a base to destroy the Ottomans for good-establishing a new middle eastern empire(call it the Alian Sultanate or something), while the industrial revolution and the age of Empire in Europe is delayed for at least two hundred years, dramatically changing world history.