Your challenge is with a POD after 1812 have no Belgian nation come into existence (note this does not invalidate a separate kingdom of Walloon however).
Is there any realistic way in the early 19th century to split Belgium up between the Netherlands and France? Because I can only see three likely outcomes for Belgium are remaining French (in a Napoleon/France does better scenario), Belgium remains Dutch (in a the Dutch beat or avoid the Belgian revolt scenario, which is not as unlikely as people here seem to think) or a Belgium becomes an independent nation after it revolts from the Netherlands. Ok, there might be a fourth scenario in which Belgium becomes Prussian, but that is quite unlikely.
Looking at the political and diplomatic situation in the early 19th century, I can see realy no way to make such an arbitrary division in splitting Flanders from Wallonia.
Both sides at Waterloo beat each other to a pulp, but retain their relative field positions at the end. The campaign evolves to a stalemate and in 1816, an armistice is signed.
France continues occupation and eventually annexes Wallonia. Flanders remains with the Netherlands
I have always been sceptical about the Talleyrand partician plan. Not only does it completely ignore the wishes of the Belgian people (which to be fair can be expected in the 19th century), it ignores Dutch history or culture (for example Zeelandic Flanders had been Dutch for century and has a protestant majority, which would end up in the Catholic freestate of Antwerp). It gives Prussia, who was not involved a major part of the Netherlands, including the Meusse border (which it had been decided 15 years before they wouldn't get for various reasons) and it gives France a good part of Belgium, which I doubt anyone wants to happen (besides France of course). Oh and don't forget that it would give Britain some major responsibilities on the continent, which it would probably want to avoid.Talleyrand's 1830 OTL partition plan. Brussels and Wallonia becomes French, Flanders becomes a British protectorate, Luxemburg becomes Prussian. In 1848 Dutch nationalist overthrow the Brits.
Both sides at Waterloo beat each other to a pulp, but retain their relative field positions at the end. The campaign evolves to a stalemate and in 1816, an armistice is signed.
France continues occupation and eventually annexes Wallonia. Flanders remains with the Netherlands
I doubt such a stalemate would accepted in the days after the Napoleonic wars, both by Napoleon, who would want his entire empire back or the allies, who want Napoleon gone. But yeah, in theory that would lead to a Flanders-Wallonia split, but it would be entirely accidental that it would split Belgium at the linguistic line. The border could easily be more to the north or south, or west (with part of Flanders French) or etc.
Both sides at Waterloo beat each other to a pulp, but retain their relative field positions at the end. The campaign evolves to a stalemate and in 1816, an armistice is signed.
Is there any realistic way in the early 19th century to split Belgium up between the Netherlands and France? Because I can only see three likely outcomes for Belgium are remaining French (in a Napoleon/France does better scenario), Belgium remains Dutch (in a the Dutch beat or avoid the Belgian revolt scenario, which is not as unlikely as people here seem to think) or a Belgium becomes an independent nation after it revolts from the Netherlands. Ok, there might be a fourth scenario in which Belgium becomes Prussian, but that is quite unlikely.
Looking at the political and diplomatic situation in the early 19th century, I can see realy no way to make such an arbitrary division in splitting Flanders from Wallonia.
Perhaps I'm oversimplifying, but had Willem I attempted to mollify French speakers and Catholics in the south, then it seems less likely that they would have had reason to rebel?
Another POD could be that the Polish Uprising does nog happen. This will enable the Russian Czar to intervene on behalf of the Dutch king as was plannen.