How much of Alsace-Lorraine? And how much of the parts not taken by Germany were German-speaking/identified?
Those are not asked in a sarcastic/hostile manner at all if they seem so-I'm genuinely curious.
Actually, the 1871 border was very close to the etnolinguistic German-French divide. But here I'm assuming that Germans, for economic and strategic reasons, and annex pretty much all of the historical provinces of Alsace and Lorraine, which had belonged to the HRE up to XVII-XVIII century, up the Maas-Meuse river. The river is not the exact historical border, it went somwhat eastward in northern Lorraine, and westward in southern Lorraine. But I'm pretty much sure that the river is the natural border that the Germans would enforce, for obvious strategic reasons.
For pretty much the same reasoning, economic and strategic concerns, I assume that Italians could go beyond the claim of Italian-speaking Nice and annex all of the French Riviera, up to Hyeres.
That's how I have set up things in my "a different 1866" TL.
Italy gets a rather more efficient government in 1861-66 (either Cavour survives, or an ATL more talented statesman emerges). As a result, Italian economy and state-building are managed rather better, and Italy reaches 1866 with a much fitter military (mostly, a better high command, since the bulk of the army and navy were actually already rather good, although the Italian army gets shaped on the Prussian model, which definitely helps). They seek a strong alliance with Prussia against Austria. The 1866 war happens.
Italy wins decisive victories on land and at sea against Austria, as good as the Prussian ones. The Austrian army is effectively destroyed, the navy is decimated, and the Italians occupy Trento and Kustenland, and land in Dalmatia. They claim all of those lands at the peace table. Spurred by their ally's success, King Wilhelm and the Prussian generals get greedy and put irresistible pressure on Bismarck to get Prussia its hefty slice of Habsburg flesh. So Otto reluctantly claims Bohemia-Moravia.
Crying foul about the balance of power, Napoleon III threatens war. With their armies massed in the East, Prussia and Italy are forced to compromise on their claims, but they do not forgive nor forget. Prussia annexes Hanover, Saxony, Austrian Silesia, and the German-majority districts of northern Bohemia-Moravia (effectively, the Sudetenland, except the parts bordering German Austria), but leaves Czechia alone. Italy annexes Veneto, Trento, and Gorizia-Gradisca, but leaves Trieste, Istria, and Dalmatia alone.
Prussian-Italian alliance is confirmed and strenghtened, France is alarmed at their growing might, and seeks a pretext to cut down the upstart duo. Austria, utterly humiliated by the defeat, slips into growing domestic unrest.
The casus belli for France comes a couple of years later, when it unsuccessfully tries to annex Luxemburg, and is vetoed by Prussia, and Italian patriots overthrow the Pope, which France protects. War explodes between France and the Italo-Prussian alliance. Despite the overconfident expectations of the French, they get their butts handed them on a plate. Austria makes moves to join France, but resistance by Pan-German nationalist opinion brings it further on the brink of revolution, so it backs down.
Prussia unifies Germany, which annexes Luxemburg, Alsace, and Lorraine, up to the Maas/Meuse. Italy annexes Savoy, Corsica, Nice, and the Riviera, up to Hyeres, as well as eastern Algeria (Oran). After doing so well twice in a row, the German-Italian partnership is solidified into an irontight strategic and economic bloc.
In the next few years, Austria further spirals into domestic unrest, as the various nationalities fight for power between themselves and against the discredited Habsburg regime. Half-baked attempts at a power-sharing compromise between Germans and Magyars flounder. Revolution explodes in Austria, soon the Habsburg empire collapses completely and is partitioned. Germany gets Austria, Bohemia-Moravia, and South Tyrol, Italy gets Trieste, Istria, and Dalmatia, Slovenia is divided between Germany and Italy, Russia gets Krakow, Galicia, and Bukovina, Galicia, Hungary is set up as an independent kingdom with Slovakia, Transylvania, Voijvodina, and a federal union with Croatia.
(I have also made a variant where the Habsburg collapse happens immediately after the F-P-I war, Franz Joseph appeals to Russia for help as in 1848, Germany and Italy canot intervene as their armies are still in France, and Russian bayonets barely stabilize the Habsburg regime, even if Austria becomes a wholly authoritarian and centralized Russian vassal, Russia still gets Galicia for its trouble, and Magyar/Pan-German nationalism simmers under the surface. But this is not the outcome I use here).
The point of this thread is that I got curious whether it might be possible to insert further gains for Germany and Italy in this TL, such as Germany getting Denmark or Netherlands-Flanders as a result of the F-P-I war.
I suspect it may be possible for Denmark to misjudge the outcome of the war completely, join France seeking a revanche for its recent defeat in the 1864 war, and be quickly curbstomped by Prussia. This would give Bismarck the perfect excuse to annex it.
Getting Belgium and Netherlands in the fray seems rather more complex. Given that controversy over Luxemburg is one of the casus belli, it might be theoretically possible to have the war expand to the Low Countries, but it seems rather more difficult. Napoleon III is already facing a two-fronts war, even if he totally underestimates Prussia and Italy, even he may have pause before violating the neutrality of Belgium, which would alienate Britain. Maybe the involvement of the Low Countries would best be left for TTL's WWI, even if at that point Germany and Italy would be allied with Britain, which would have strong qualms about a German-Dutch-Flemish union.
Anyway, the TL continues with the onset of the attack of Russia to Turkey. The war is a success, and the Russians armies get in sight of Constantinople, but Britain, scared by Russian control of the Straits, threatens war, soon backed by Germany and Italy.
Bourbon France, which has a Carlist dynastic claim on the throne of Spain, sponsors a Carlist coup in Spain, and a French-Spanish dynastic union is formed.
An international conference is called in the Hague. As pretty much every power but Britain is burdened by war fatigue at this point, there is no great willingness to fight a general war, so reluctantly, a last-ditch compromise is reached.
Russia gains southern Bessarabia and the districts of
Ardahan, Artvin, Batum, Kars, Olti, and Beyazit, Romania gets independence and northern Dobruja, Serbia gets independence and a northern slice of Kosovo, Bulgaria gets self-rule in OTL modern borders, Greece gains Thessaly and southern Epirus, Britain gets Cyprus, Italy gets a sphere of influence in Tunisia and Libya, Crete is put under the administration of the Great Powers, Bosnia becomes a self-ruling principality under a sovreign picked by the powers. Montenegro gets independent under an Italian protectorate. The Ottomans keep Albania, Macedonia, most of Kosovo, and Thrace, and they are bound by the powers to enact a strrong set of capitulations and internal reform for their Christian subjects. The powers proscribe every state and principality from enacting abuses on their minorities. France gets assent for its dynastic union with Spain.
France-Spain, slowly recovering from the defeat, and seeking support for revenge against the German-Italian bloc, signs the Dual Entente with Russia (and Austria in the variant TL), building a bloc of reactionary-authoritarian powers. Britain, still wary of Russian expansionism, makes the Quadruple Alliance with Germany, Italy, and Hungary.
I expect that German annexation of Denmark, if it happens as result of Danish intevention in the F-P-I war, would not trouble Britain overmuch. Its main strategic result is that Germany is even more able to keep Russia trapped in the Baltic, after all. German expansion in the Low Countries is a much more serious issue and could create long-term antagonism between Britain and the Italo-German bloc.
I'm not sure at all how Italo-German partition of Switzerland could fit in this TL.